Combination Chair
DESCRIPTION 
     1. Technical Field 
     The present invention relates to a combination chair which can be used as one chair by combining a plurality of chairs. 
     2. Background Art 
     In a dining room, for example, a table and a plurality of chairs are provided. Usually, the chairs are prepared so as to correspond to the number of members in the family. Therefore, in the case where there is a guest or the like, and the number of people using the dining room increases, the number of chairs must be increased in accordance with the number of guests added. 
     It is possible that extra chairs are always prepared for guests in advance; however extra chairs occupy some space in the room. Therefore, when they are not used, they take up much space. In a house of a narrow living space, it is, in many cases, difficult to reserve a space for placing extra chairs. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a combination chair, in which a plurality of chairs are stacked up into one chair, or vice versa, and therefore the number of chairs can be increased or decreased in accordance with an increase or decrease in number of people using chairs, thus avoiding the occupation of an extra space. 
     Another object of the present invention is to provide a combination chair in which chairs, when they are stacked up, can be combined into one chair without looseness. 
     According to an embodiment of the present invention, there is provided a combination chair comprising a plurality of chairs, characterized in that: said plurality of chairs each having a seat portion supported by legs and a backrest provided on the seat portion, and the backrests of the chairs are jointed to be adjacent to each other by one side in the width direction, and lengths of the legs are set so that lower ends thereof coincide with each other. 
     According to another embodiment of the present invention, there is provided a combination chair comprising a plurality of chairs, characterized in that each of the chairs has a seat portion supported by legs and a backrest provided on the seat portion, the seat portion of each chair is supported by said legs at such a height that the seat portions are stacked one upon another in an up-and-down direction, and inner surfaces of the legs of a chair situated on an upper side are fitted to outer surfaces of the legs of a chair situated on a lower side when the chairs are combined so that the seat portions are stacked up. 
     According to still another embodiment of the present invention, there is provided a combination chair comprising of a plurality of chairs, characterized in that each of the chairs has a seat portion supported by legs and a backrest provided on the seat portion, the backrest of a chair whose seat portion is located on an upper side, and the backrest of a chair whose seat portion is located on a lower side is fitted in a frame of the backrest of the chair whose seat portion is located on the upper side when said plurality of chairs are combined so that the seat portions thereof are stacked up in the up-and-down direction. 
     With the above-described structures, a plurality of chairs can be used separately as a single chair, and they can be combined together to be used as one chair. Therefore, the present invention can follow an increase/decrease in the number of users. 
     When the plurality of chairs are combined together, the slipping movement in the up-and-down direction and horizontal direction can be suppressed, and therefore the combination chair can be easily used as one chair. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS 1A, 1B and 1C are perspective views of a combination chair according to the first embodiment of the present invention, 
     FIG. 1A being a perspective view showing a first chair, 
     FIG. 1B being a perspective view showing the first and second chairs while being stacked up, and 
     FIG. 1C being a perspective view showing the first and second chairs which have been stacked up; 
     FIGS. 2A and 2B show the first chair, 
     FIG. 2A being a plan view thereof and 
     FIG. 2B being a front view thereof; 
     FIGS. 3A and 3B show the second chair, 
     FIG. 3A being a plan view thereof and 
     FIG. 3B being a front view thereof; 
     FIGS. 4A and 4B show the first and second chairs combined, 
     FIG. 4A, being a plan view thereof and 
     FIG. 4B being a front view thereof; 
     FIGS. 5A, 5B and 5C show a seat portion of the chairs, 
     FIG. 5A being a plan view of a lower surface side of the seat, 
     FIG. 5B being a side view of the seat taken along the line 5B--5B in FIG. 5A, and 
     FIG. 5C being a cross section taken along the line 5C--5C in FIG. 5A; 
     FIG. 6 is a side view of a front leg; 
     FIG. 7 is a side view of a rear leg; 
     FIGS. 8A and 8B show a modified version of the first embodiment, 
     FIG. 8A being a plan view showing three chairs are combined and 
     FIG. 8B being a front view of such a combination; 
     FIGS. 9A, 9B and 9C are perspective views of a combination chair, according to the second embodiment of the present invention, 
     FIG. 9A being a perspective view showing a first chair, 
     FIG. 9B being a perspective view showing a second chair, and 
     FIG. 9C being a perspective view showing the first and second chairs when they have been combined together; 
     FIG. 10 is a cross section of the combination chair taken along the line 10--10 in FIG. 9C; 
     FIG. 11 is a cross section of the combination chair taken along the line 11--11 in FIG. 9C; 
     FIG. 12 is a perspective view showing a portion of seat portions of the two chairs combined, a part of which is cutaway; 
     FIG. 13 is a cross section of the seat portion of the combination of the two chairs; 
     FIG. 14 is an explanatory view illustrating the state of the front leg and rear leg of the combination chair; 
     FIGS. and 15A, 15B, 15C are perspective views of a combination chair according to the third embodiment of the present invention, 
     FIG. 15A being a perspective view showing a first chair, 
     FIG. 15B being a perspective view showing a second chair, and 
     FIG. 15C being a perspective view showing the first and second chairs when they have been combined together; 
     FIG. 16 is a vertical section of the first and second chairs combined; 
     FIG. 17 is a perspective view of a cover of the combination, partially showing a cross section thereof; 
     FIG. 18 is a cross section of the combination taken along the line 18--18 in FIG. 16; 
     FIG. 19 cross section of a remodeled version of the third embodiment, in which three chairs are stacked up; 
     FIGS. 20A, 20B, 20C and 20D are perspective views of a combination chair according to the fourth embodiment of the present invention, 
     FIG. 20A being a perspective view showing a first chair, 
     FIG. 20B being a perspective view showing a second chair, 
     FIG. 20C being a perspective view showing the first and second chairs when they have been combined together, and 
     FIG. 20D being a cross section of legs of the combined chair; 
     FIGS. 21A to 21K are cross sections of front legs of different versions; 
     FIGS. 22, 22B, and 22C are perspective views of a combination chair according to the fifth embodiment of the present invention, 
     FIG. 22A being a perspective view showing first and second chairs which have been combined, 
     FIG. 22B being a perspective view showing the first chair, and 
     FIG. 22C being a perspective view showing the second chair; 
     FIG. 23 is a front sectional view, along the line 23--23 in FIG. 22A, showing a seat portion of the first and second chairs combined; 
     FIG. 24 is a lateral cross section, along the line 24--24 in FIG. 22A, of a seat portion and a backrest of the combination of the first and second chairs; 
     FIG. 25 is a perspective view showing a combination of first and second chairs, according to the sixth embodiment of the present invention; 
     FIG. 26A is a front view of the first chair of the combination; 
     FIG. 26B is a bottom view of the first chair of the combination; 
     FIG. 27A is a front view of the second chair of the combination; 
     FIG. 27B is a bottom view of the second chair of the combination; 
     FIG. 28A is a side view of a first chair of a combination chair according to the seventh embodiment of the present invention; 
     FIG. 28B is a side view of a second chair thereof; 
     FIG. 29A is a front view showing the first and second chairs which have been combined; and 
     FIG. 29B is a front view showing the first and second chairs combined. 
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present invention will now be described with reference to drawings. 
     FIGS. 1 to 7 show the first embodiment of the present invention. A combination chair according to the first embodiment comprises two chairs, as shown in FIGS. 1A to 1C, 2A, 2B, 3A and 3B, more specifically, a first chair 1a and a second chair 1b having different shapes (in terms of measurements) though they appear to be substantially identical. 
     The first and second chairs 1a and 1b include disk-shaped seat portions 2a and 2b of the same size, respectively. Each of the seat portions 2a and 2b is supported by four legs 3a and 3b at a predetermined height. 
     Each of the seat portions 2a and 2b is jointed to the legs 3a and 3b as shown in FIGS. 5A to 5C. More specifically, two L-shaped grooves 4 bare formed on the lower surface of each of the seat portions 2a and 2b as shown in FIG. 5A. The L-shaped grooves 4 abut each other at their outer edges of angle portions at the center of each of the seat portions 2a and 2b, and the ends of the L-shaped grooves are opened to the outer surfaces of the seat portions 2a and 2b in the circumferential direction at an interval of 90 degrees. Within the angle portion of each L-shaped groove 4, a step portion 5 having a width of about a half of that of the groove 4 and a height of about a half of the depth of the groove 4, is formed to project. 
     Of the legs 3a and 3b, each of two front legs 3a-2, 3b-2 has a joint portion 6 which is made substantially horizontal by bending a wood or metal material into an L-shape, and a support portion 7 which is substantially vertical as shown in FIG. 6. The end of the joint portion 6 is cut at an angle of 45 degrees to be a fit portion 8 as shown in FIG. 5A, and the upper surface thereof has a recess portion 9 which engages with the step portion 5. 
     Among the legs 3a and 3b, the joint portions 6 of a pair of the front legs 3a-2 and 3b-2 are inserted respectively into one and the other ends of each one of the L-shaped grooves 4, so that each recess portion 9 engages with the corresponding one of step portions 5. Thus, the fit portions 8 of the ends of a pair of the joint portions 6 are placed to match with each other, and while maintaining the matching state, the pair of the front legs 3a-2 and 3b-2 are fixed to that one of the L-shaped grooves 4 by screws or adhesive (not shown). With this structure, the support portions 7 of the pair of front legs 3a-2 and 3b-2 project downward from the outer circumferential surface of each of the seat portions 2a and 2b. 
     A pair of rear legs 3a-1 and 3b-1 have a structure as shown in FIG. 7, in which a joint portion 6, a support portion 7 and a mount portion 12 comprising backrests 11a and 11b, are integrated into one body. More specifically, the support member 7 and the mount portion 12 are made from one piece material, and the joint portion 6 is integrated by its one end portion to the material at the mid portion thereof, so as to project substantially horizontally therefrom. 
     The joint portions 6 of each pair of rear legs 3a-1 and 3b-1 are inserted into the other one of the L-shaped grooves 4 of each of the seat portions 2a and 2b. Thus, the pair of the rear legs are fixed to the groove in the same manner as for the front legs. 
     On the upper side of each of a pair of the mount portions of each of the chairs 1a and 1b, a back plate 13 bent along the circumferential direction of the corresponding seat portion 2a and 2b is provided so as to be angled in a range of about 90 degrees in the circumferential direction of the corresponding seat portion 2a or 2b. 
     With regard to four legs 3a and 3b of the first and second chairs 1a and 1b, two rear legs 3a-1 and 3b-1 and two front legs 3a-2 and 3b-2 are placed to be located on both ends of the circumferential direction within two regions which point symmetrical, in the case where each of the disk-shaped seat portions 2a and 2b is divided into four areas a to d by two lines X and Y normally crossing with each other as shown in FIGS. 2A and 3A. 
     The arrangement of the four legs 3a and 3b of the first chair 1a is the same as that of the second chair 1b. FIGS. 3A and 3B show the state with reference to that shown in FIGS. 2A and 2B, that is, FIGS. 3A and 3B illustrate that the second chair 1b is rotated by 90 degrees with respect to the first chair 1a. 
     When the two rear legs 3a-1 of the first chair 1aare located in the area d as shown in FIG. 2A, the front legs 3a-2 are automatically located in the area b, whereas when the two rear legs 3b-1 of the second chair 1b are located in the area a as shown in FIG. 3A, the front legs 3b-2 are automatically located in the area c. 
     The first and second chairs 1a and 1b differ from each other in the height of supporting each of the seat portions 2a and 2b. More specifically, as shown in FIG. 2B and FIG. 3B, where H1 represents the height of the seat portion 2a of the first chair 1a, and H2 represents the height of the seat portion 2b of the second chair 1b, the relationship therebetween is H1&lt;H2. The measurements of the supporting members 7 of the legs 3a and 3b of the first and second chairs 1aand 1b are determined so that the difference in height (H2-H1) is substantially the same as the thickness of the seat portion 2b of the second chair 1b. 
     With regard to the backrests 11a and 11b of the first and second chairs 1a and 1b, the lengths of the mount portions 12 are determined so that the upper ends of the back plates 13 of the chairs 1a and 1b are leveled. More specifically, the length of the mount portion 12 of the first chair 1a is set larger than that of the mount portion 12 of the second chair portion 1b by the thickness of the seat portion 2b of the second chair 1b. 
     According to the combination chair having the above-described structure, each of the first chair 1a and the second chair member 1b can be independently used as a chair. For example, when two pairs of combination chairs are prepared, four chairs can be used for four people. 
     In contrast, when the number of users reduces from four to two, each of the first chairs 1a is stacked upon the corresponding one of the second chairs 1b, thus reducing the number of chairs from four to two. 
     More specifically, as shown in FIGS. 1B, 2A and 3A, the seat portion 2b of the second chair 1b is stacked upon the seat portion 2a of the first chair member 1a in such a manner that the seat portion 2b is rotated by 90 degrees in the clockwise direction with respect to the seat portion 2a. With this operation, the backrest 11a of the first chair 1a and the backrest 11b of the second seat portion 1b are placed adjacent to each other with one end of the backrest 11a being in contact with one end of the backrest 11b, thus surrounding a part of the seat portions 2a and 2b in a range of 180 degree in the circumferential direction. Therefore, the two backrests 11a and 11b appear to be one backrest as a whole. 
     Further, one of the front legs 3b-2 of the second chair 1b is placed to be adjacent to and in contact with one of the front legs 3a-2 of the first chair la, and the other front legs 3a-2 and 3b-2 are placed to be adjacent to and in contact with one of the rear legs 3b-1 of the second chair 1b and one of the rear legs 3a-1 of the first chair la, respectively. The two legs placed to be in contact with and adjacent to each other have an appearance of one leg, and such a structure is good in appearance. 
     As described above, with a structure in which the backrests 11a and 11b and the front and back legs 3a and 3b are placed to be adjacent to and in contact with each other, the second chair 1b is prevented from rotating with respect to the first chair a in the circumferential direction, and thus the first chair is integrally stacked upon the second chair. 
     When the lower surface of the seat portion 2b of the second chair 1b is stacked upon the upper surface of the seat portion 2a of the first chair la, the lower ends of the legs 3a and 3b of these chairs are located at the same position, more specifically, to coincide with each other. With this structure, the legs 3a and 3b of both chairs 1a and 1b are grounded on the floor, and therefore the stacked two chairs 1a and 1b are not rendered loose, since the second chair 1b whose seat portion 2b is placed on the upper side, is not set unstable. 
     Further, the joint portions 6 of the rear legs 3a-1 and 3b-1 and the front legs 3a-2 and 3b-2 are embedded in the grooves 4, and the support portions 7 are rendered to project from the outer circumferences of the seat portions 2a and 2b. With this structure, these legs do not project from the lower surfaces of the seat portions 2a and 3b. Consequently, when the lower surface of the seat portion 2b of the second chair 1b is stacked upon the upper surface of the seat portion 2a of the first chair 1a, these seat portions can be accurately jointed together without looseness. 
     As described above, the combination chair of the present invention is not simply a chair formed by stacking the first chair 1a upon the second chair 1b, but the combination chair has an appearance as if it is one chair, with the structure in which the seat portions 2a, 2b, the legs 3a and 3b, and the backrests 11a and 11b are jointed up to down and side to side. Therefore, even if two chairs 1a and 1b are used as one chair, the appearance of such a combination chair is natural, and in fact, excellent, and the combination chair can be easily used. 
     Further, with the structure in which the two backrests 11a and 11b are jointed side by side, the two backrests can be used not only as a backrest, but also as an armrest. 
     FIG. 8 shows a remodeled version of the first embodiment. In this version, first to third chairs 1a, 1b and 1c are stacked up into one combination chair. In the following description, structural elements of the first and second chairs 1a and 1b, which are the same as those of the above-described first embodiment, are designated by the same reference numerals, and a seat portion, legs and a backrest of the third chair 1c are designated by 2c, 3c and 11c, respectively. 
     In order to achieve the following constitution of the three chairs 1a to 1c, the chairs are formed as described as follows. That is, the lengths of the legs 3b and 3c of the second and third chairs 1b and 1c are determined so that the legs 3b and 3c are both grounded when the seat portions 2a to 2c of the chairs 1a to 1c are stacked up together. The backrests 11a to 11c are formed so that they are leveled at the same height when the chairs are stacked up together. Further, the three backrests 11a to 11c are formed so that they cover a range of about 180 degrees of the outer circumferences of the seat portions 2a to 2c, with each backrest covering a range of 60 degrees in the circumferential direction of its seat portion, when the three backrests 11a to 11c are placed adjacent to each other. 
     With the above-described constitution, the number of chairs can be changed from one to three or vice versa, in accordance with a change in the number of users, and therefore the range of usage is further expanded as compared to the case where two chairs are combined, thus increasing the utility of the chair combination. 
     In the above first embodiment, the description was provided in connection with the case where the seat portions of chairs are of a round shape; however the seat portions may be of a shape other than a round type, such as a rectangular type including square or a hexagonal type. 
     FIGS. 9 to 14 show the second embodiment of the present invention. The combination chair of the second embodiment comprises two chairs, more specifically, a first chair (main chair) 21a and a second chair (sub-chair) 21b, which appear to be substantially the same, but are different from each other in shape (measurements). 
     The first and second chairs 21a and 21b have rectangular seat portions 22a and 22b having different sizes from each other. More specifically, the seat portion 22a of the first chair 21a is formed in a rectangular shape which is larger than the size of the seat portion 22b of the second chair 21b. 
     As shown in FIGS. 10 and 11, the seat portions 22aand 22b comprise frame bodies 25a and 25b in which cushion members 24a and 24b are provided on the upper surfaces of rectangular seat plates 23a and 23b, and the circumference excluding the back surfaces of the seat plates 23a and 23b are covered from three directions; two pairs of front legs 26a and 26b, the upper ends of which are jointed to the two corner portions on the front end sides of the seat portions 22a and 22b; two pairs of rear legs 27a and 27b, the mid-portions of which are jointed to the corner portions of the rear end sides of the seat portions 22a and 22b; and backrests 29a and 29b formed by providing two back plates 28a and 28b on the portions of the rear legs 27a and 27b, which project from the upper surfaces of the seat portions 22a and 22b, in the vertical direction at a predetermined interval. 
     The seat portion 22a of the first chair 21a is formed and set at a predetermined height so that the seat portion can be stacked upon the upper surface side of the seat portion 22b of the second chair 21b. More specifically, the lengths of these legs and the height at which the seat portions 22a and 22b are supported are determined so that the front legs 26a and rear legs 27a of the first chair 21a are grounded when the seat portion 22a of the first chair 21a is stacked upon the upper surface side of the seat portion 22b of the second chair 21b. 
     Both sides of the frame portions 25a and 25b of the seat portions 22a and 22b are tilted so that the width between both sides is decreased from the front end to the rear end as shown in FIGS. 13 and 14. The angle of tilt is expressed by 8. With this structure, the movement of the second chair 21b is integrally associated with the movements of the first chair 21a in the front and rear directions when the seat portion 22b of the second chair 21b is stacked upon the seat portion 22a of the first chair 21a. In other words, the second chair 21b is prevented from moving separately from the first chair 21a. 
     Each of the two front legs 26a of the first chair 21a and the two front legs 26b of the second chair 21b has an L-shaped cross section as shown in FIG. 14. The measurement between the outer surfaces of the two front legs 26b of the second chair 21b is set slightly smaller than the measurement between the inner surfaces of the two front legs 26a of the first chair 21a. 
     Each of the two rear legs 27a of the first chair 21a and the two rear legs 27b of the second chair 21b has a strap-shaped cross section as shown in FIG. 14. The measurement between the outer surfaces of the two front legs 26b of the second chair 21b is set slightly smaller than the measurement between the inner surfaces of the two front legs 26a of the first chair 21a. 
     Therefore, when the first chair 21a is stacked upon the second chair 21b, the front legs 26b and rear legs 27b of the second chair 21b are placed at positions to engage with the inner surfaces of the front legs 26a and the rear legs 27a of the first chair 21a. Thus, the second chair 21b is combined with the first chair 21a without being shaky in the lateral direction. 
     The depth of the first chair 21a is set slightly larger than the depth of the second chair 21b. With this structure, when the first chair 21a is stacked upon the second chair 21b, a pair of the rear legs 27b of the second chair 21b are fitted between a pair of the rear legs 27a of the first chair 21a. 
     As shown in FIGS. 9A and 9B, the width a of the back plates 28b of the second chair 21b is set slightly smaller than the width b of the portions of the pair of the rear legs 27a of the first chair 21a, which project upward from the seat portion 22a, on which the backrest 29a is formed. 
     As the pair of the rear legs 27b of the second chair 21b are fitted between the inner sides of the pair of the rear legs 27a of the first chair 21a, the back plates 28b of the second chair 21b are also fitted between the rear legs 27a of the backrests 29a of the first chair 21a. Therefore, as shown in FIG. 11, the back plates 28a of the first chair 21a and the back plates 28b of the second chair 21b coincide substantially with each other in terms of the front-rear direction, that is, the back plates are flush with each other and the back plates 28a of the first chair 21a are engaged with the back plates 28b of the second chair 21b in the up-and-down direction. 
     According to the combination chair having the above-described structure, each of the first chair 21a and the second chair 21b can be used separately as a chair. For example, with two pairs of combination chairs, four people can use four chairs. 
     When the number of users decreases from four to two, four chairs can be set into two chairs by stacking the first chair 21a of each pair upon the second chair 21b. 
     As shown in FIGS. 9C, 10 and 11, the seat portion 22a of the first chair 21a is stacked upon the seat portion 22b of the second chair 21b. With this operation, two chairs, namely the first and second chairs 21a and 22b are combined into one chair. Further, the front legs 26b and the rear legs 27b can be set in the inner sides of the front legs 26a and the rear legs 27a of the first chair 21a, and the back plates 28b of the backrest 29b of the second chair 21b can be engaged with the back plates 28a of the backrest 29a of the first chair 21a in the up-and-down direction. Furthermore, as the seat portions 22a and 22b are stacked one upon the other, they are integrally combined with each other. 
     With the above-described structure and operation, not only the first chair 21a and the second chair 21b can be combined into one chair, but also they are integrated with each other and a shaky movement thereof in the width direction or the front-rear direction, or even the up-and-down direction can be prevented. Consequently, such a combination chair can be easily used as one chair. 
     Moreover, since the front legs 26a and the rear legs 27b of the second chair 21b are fitted between the inner sides of the front legs 26a and the rear legs 27a of the first chair 21a, these legs exhibit an appearance of integrated sets. Also, the seat portion 22b of the second chair 21b is covered by the seat portion 22a of the first chair 21a, and the backrest 29a of the first chair 21a and the backrest 29b of the second chair 21b exhibit an appearance of integrated sets as the back plates 28a and 28b are flushed with each other. Therefore, the two chairs, namely, the first and second chairs 21a and 21b set in combination exhibit an excellent appearance as if they are one chair. 
     In order to separately use the two chairs 21a and 21b set in combination as shown in FIGS. 10 and 11, the first chair 21a is held upward to release the combination state with the second chair 21b, thus separating these chairs from each other. 
     FIGS. 15 to 18 show the third embodiment of the present invention. The difference between this embodiment and the second embodiment can be identified by comparing the backrest structures of the first chair 1a and the second chair 1b of this embodiment with those in the second embodiment. Structural elements of this embodiment, which are the same as those of the second embodiment, are designated by the same reference numerals, and the explanations therefor will be omitted. 
     Backrests 39a and 39b of chairs 21a and 21b of this embodiment are formed by setting back plates 38a and 38b on the upper portions of rear legs 27a and 27b, respectively. With this structure, when the first chair 21a and the second chair 21b are combined together, the backrest 39a of the second chair 21b is jointed to the back surface side of the backrest 39a of the first chair 21a as shown in FIG. 16, and the backrest 39b of the second chair 21b is fitted in the backrest 39a of the first chair 21a inwardly in the width direction of the backrest 39a as shown in FIG. 18. 
     With the engagement between the backrests 39a and 39b, the width directional movement of the first chair 21a and the second chair 21b is limited. The up-and-down directional movement of the pair of the chairs 21a and 21b can be limited by integrally jointing the seat portions 22a and 22b of the combined first and second chairs 21a and 21b, with a cover 31, as shown in FIG. 17. 
     The cover 31 has a rectangular bag-like structure having an open lower surface, made of a material formed by covering a seat-like cushion material with fabric, and a first velvet fastener 32 is set on the lower end portion of each side of the cover. In contrast, a second velvet fastener (not shown) to be engaged with the first velvet fastener 32 is set on the inner surface of a frame body 23b of the seat portion 22b of the second chair 21b. 
     With this structure, as shown in FIG. 16, after the first chair 21a and the second chair 21b are combined together, the seat portion 22a of the first chair 21a is covered by the cover 31, and the first velvet fastener 32 provided at the lower end of each side is engaged with the second velvet fastener provided on the inner surface of the seat portion 22b of the second chair 21b, thus integrally combining the first chair 21a and the second chair 21b. Therefore, the movement not only in the up-and-down direction, but also in the horizontal direction, can be suppressed. Further, the two seat portions 22a and 22b covered by the cover 31 have an appearance as if it is one seat portion, and therefore exhibit a natural appearance. 
     FIG. 19 is a remodeled version of the second embodiment. The second embodiment was described in connection with the case where two chairs are combined; however this version is directed to a combination chair in which first to third chairs 21a, 21b and 21c are stacked up together. 
     This version will now be described with reference to FIG. 19. The same structural elements as those of the second embodiments are designated by the same reference numerals, and the seat portion of the third chair 21c is denoted by 22c, the front legs are denoted by 26c, the rear legs by 27c and the backrest by 29c. 
     In the case of the structure in which three chairs 21a to 21c can be combined together, the lengths of the front legs 26a, 26b and 26c and the rear legs 27a, 27b and 27c are determined so that each of these legs are grounded when the seat portions 22a to 22c of the chairs 21a to 21c are stacked up, and the widths of the backrests 39a to 39c are determined so that the back plates 28a to 28c are fitted with each other in the up-and-down direction, being flush with each other, as in the second embodiment. 
     With the above-described structure, the number of chairs used can be changed to one, two or three in accordance with an increase/decrease in the number of users. Therefore, the range of use is expanded as compared to the case where two chairs are combined, thus increasing the utility. 
     FIGS. 20A to 20D show the fourth embodiment of the present invention. This embodiment is substantially the same as the first embodiment except for the following points. That is, the cross sections of the front legs 26a and 26b and the rear legs 27a and 27be of the first chair 21a and the second chair 21b have strip-like (rectangular) shapes, and each pair of front legs 26a and 26b are arranged so that the front end sides thereof are tilted inwardly in the width direction, and each pair of rear legs 27a and 27b are arranged in parallel with each other in the front-to-rear direction, as shown in FIG. 20D. 
     With the above structure, when the first chair 21a and the second chair 21b are combined together, the outer surfaces of the front legs 26b and the rear legs 27b of the second chair 21b are jointed to the inner surfaces of the front legs 26a and the rear legs 27a of the first chair 21a. Thus, the shaky movement of the second chair 21b in the right-to-left direction and the front direction with respect to the first chair 21a is suppressed. 
     FIGS. 21A to 21K are cross-sections illustrating a state in which the front legs 26a of the first chair 21a are engaged with the front legs 26b of the second chair 21b. As shown in these figures, the front legs can be arranged to have various shapes in cross section. 
     Of FIGS. 21A to 21K, those except for the version shown in FIG. 21G show the cases where the front legs 26b of the second chair 21b are engaged with the inner sides, in terms of the width direction, of the front legs 26a of the first chair 21a. Thus, the width-directional shaky movement of the two combined chairs 21a and 21b can be suppressed. In contrast, the version shown in FIG. 21G is directed to the case where the front legs 26b of the second chair are located on the rear sides, in terms of the front-rear direction, of the front legs 26a of the first chair 21a. Thus, the shaky movement of the combined two chairs 21a and 21b in the front-rear direction is suppressed. 
     The second to fourth embodiments were described in connection with the case where the seat portion of the chair is of a square shape; however the seat portion may be of a shape other than square, such as a round shape. 
     FIGS. 22 to 24 show the fifth embodiment of the present invention. 
     A combination chair of this embodiment comprises two chairs, namely, a first chair (main chair) 41a and a second chair (sub-chair) 41b, which differ from each other in appearance and shape (measurements), as shown in FIGS. 22A and 22B. 
     The first chairs 41a and 41b respectively include rectangular seat portions 42a and 42b which are different from each other in size. More specifically, the seat portion 42a of the first chair 41a has a rectangular shape whose width is larger than and whose length is about the same as that of the seat portion 42b of the second chair 41b. 
     The seat portions 42a and 42b are formed by providing cushion members 44a and 44b on the upper surfaces of rectangular seat plates 43a and 43b, respectively, as shown in FIGS. 23 and 24. Two front legs 46a and 46b are jointed by their upper end portions to two corners of the front end side of each of the seat portions 42a and 42b, and two rear legs 47a and 47b which are connected to each other by their mid portions, are jointed to two corner portions of the rear end side. 
     The portion of the rear legs 47a of the first chair 41a, which project upward from the seat portion 42a, is formed into a frame-like backrest 49a. A cushion member 50 is provided via a back plate 51 on the front surface of the portion of the rear legs 47b of the second chair 41b, which project upward from the seat portion 42b, thus forming a rectangular backrest 49b. The size of the backrest 49b of the second chair 41b is determined so as to fit to the frame of the backrest 49a of the first chair 41a. Across the portions of the pair of the rear legs 47b, which correspond to the lower end portion of the back plate 51, a lateral bar 52 is bridged so as to reinforce the back plate 51 as shown in FIG. 24. 
     The size and height of the seat portion 42a of the first chair 41a are set so that it can be stacked upon the upper surface side of the seat portion 42b of the second chair 41b. More specifically, the heights for the seat portions 42a and 42b, that is, the lengths of the legs, are determined so that the front legs 46a and rear legs 47a of the first chair 41a are grounded on the floor when the seat portion 42a of the first chair 41a is stacked upon the upper surface side of the seat portion 42b of the second chair 41b. 
     Each of the two front legs 46a of the first chair 41a and the two front legs 46b of the second chair 41b has a rectangular shape in cross section, that is, a stripe shape, as shown in FIGS. 22A to 22C. The measurement between the outer surfaces, in terms of the width direction, of the two front legs 46b of the second chair 41b is set slightly smaller than that between the inner surfaces, in terms of the width direction, of the two front legs 46a of the first chair 41a. 
     Each of the two rear legs 47a of the first chair 41a and the two rear legs 47b of the second chair 41b has a rectangular shape in cross section as in the front legs. For these rear legs, the measurement between the outer surfaces, in terms of the width direction, of the two rear legs 47b of the second chair 41b is set slightly smaller than that between the inner surfaces of the two rear legs 47a of the first chair. 
     Therefore, when the first chair 41a is stacked upon the second chair 41b, the front legs 46b and the rear legs 47b of the second chair 41b are engaged with the inner sides of the front legs 46a and the rear legs 47a of the first chair 41a, and the backrest 49b of the second chair 49b is set in the frame of the backrest 49a of the first chair 41a so that the cushion 50 of the second chair protrudes to the front surface side. Thus, the second chair 1b can be combined with the first chair 1a without being loose. 
     According to such a combination chair having the above-described structure, each of the first and second chairs 41a and 41b can be separately used as a chair. For example, when two pairs of combination chairs are prepared, four people can sit on four chairs. 
     When the number of users decreases from four to two, the number of chairs can be reduced from four to two by stacking up the first and second chairs 41a and 41b of each pair together. 
     More specifically, as shown in FIGS. 22A, 23 and 24, the seat portion 42a of the first chair 41a is stacked upon the seat portion 42b of the second chair 41b. With this operation, the two chairs, namely, the first and second chairs 41a and 41b can be combined into one chair. Further, the front legs 46b and the rear legs 47b of the second chair 41b are placed on the inner sides, in terms of the width direction, of the front legs 46a and the rear legs 47a of the first chair 41a, and the backrest 49b of the second chair 41b is fitted in the frame of the backrest 49a of the first chair 41a. 
     Therefore, not only the first chair 41a and the second chair 41b are combined into one chair, but also they are integrated as a combined body without being loose. Thus, the combination chair can be easily used. 
     Further, with the structure in which the front legs 46b and the rear legs 47b of the second chair 41b are set in the inner sides, in terms of the width direction, of the front legs 46a and the rear legs 47a of the first chair 41a, these legs have an appearance as if they are integrated as each pair. Also, as the backrest 49b of the second chair 41b is set in the frame of the backrest 49a of the first chair 41a, these backrests exhibit an appearance of an integrated member. Consequently, the combined two chairs can be easily used as one chair. Furthermore, in the combination state, the cushion 50 of the backrest 49b of the second chair 41b protrudes to the front surface side of the backrest 49a of the first chair 41a, and therefore the user can lean on the cushion 50. 
     With regard to the fifth embodiment, the front legs 46a of the first chair 41a and the front legs 46b of the second chair 41b may be formed to have a shape in cross section and an arrangement as shown in any one of FIGS. 21A to 21K. 
     The fifth embodiment was described in connection with the case where the seat portion of the chair has a square shape; however the shape of the seat portion may be round, or of that other than square, such as rectangular. 
     FIGS. 25 to 27 show the sixth embodiment of the present invention. 
     A combination chair of this embodiment consists of a first chair 61a and a second chair 61b, which are substantially similar to each other in the shape of appearance. 
     The first and second chairs 61a and 61b have seat portions 62a and 62b made of substantially rectangular plate members having sizes different from each other. More specifically, the seat portion 62a of the first chair 61a has a rectangular shape larger than that of the seat portion 62b of the second chair 61b. 
     Two front legs 63a and two front legs 63b are provided at two corner portions of the front end sides of the seat portions 62a and 62b, respectively, and two front legs 64a and two front legs 64b are provided at corner portions of the rear end sides. The distance between the inner sides of a pair of the rear legs 64b of the second chair 61b is set slightly smaller than the distance between the outer sides of a pair of the rear legs 64b of the first chair 61a. 
     The seat portion 62b of the second chair 61b is set at such a height that it is fitted under the lower surface side of the seat portion 62a of the first chair 61a. With this structure, the upper surface of the seat portion 62b of the second chair 61b is jointed to the lower surface of the seat portion 62a of the first chair 61a. The lengths of the front legs 63a and the rear legs 64a of the first chair 61a are determined so that the lower ends thereof are grounded on the floor without floating. Therefore, when the first chair 61a and the second chair 61b are combined together, these chairs are not loose. 
     Each of the front legs 63a of the first chair 61a has a semi-circular shape in cross section, and each front leg is arranged so that the flat surface side thereof opposes to the rear leg 64a located in a diagonal direction of the seat portion 62a. Each of the front legs 63b of the second chair 61b has a slender rectangular shape in cross section, and is arranged so that the longitudinal direction thereof faces in the diagonal direction of the seat portion 62b. 
     The portions of the rear legs 64a and 64b of the chairs 61a and 61b, which project upward from the seat portions 62a and 62b are respectively formed into arch-shaped backrests 65a and 65b. The size of the backrest 65b of the second chair 61b is determined so that the backrest is fitted in the arch of the backrest 65a of the first chair 61a as shown in FIG. 25. In the state in which the backrest is fitted in the arch, the shaky movement of the backrest 64b of the second chair 61b in the up-and-down and right-to-left directions can be suppressed by the backrest 65a of the first chair 61a. 
     A frame body 66a is provided on the lower surface of the seat portion 62a of the first chair 61a to cover three directions of the seat portion, excluding one side, which is the rear side, and similarly, a frame body 66b is provided on the lower surface of the seat portion 62b of the second chair 61b in three directions of the seat portion, excluding one side, which is the rear side. 
     The tip end sides of the front legs 63n of the second chair 61b protrude to the outer circumference of the frame body 66b. When the first chair 61a and the second chair 61b are combined together, the tip ends of the front legs 63b of the second chair 61b are brought into contact with the flat surfaces of the front legs 63a of the first chair 61a. With this structure, the shaky movement of the second chair 61b in the front-rear direction with respect to the first chair 61a can be suppressed. 
     According to the combination chair of the above-described structure, the first chair 61a and the second chair 61b, when they are combined, can be used as one chair. 
     The first chair 61a and the second chair 61b combined are integrated together as the backrest 64b of the second chair 61b is fitted in the backrest 64a of the first chair 61a, and these backrests exhibit an appearance as if they are one. 
     When the seat portions 62a and 62b of the two chairs are combined together, the shaky movement of the second chair 61b in the front-rear, right-to-left and up-and-down directions with respect to the first chair 61a is suppressed. Further, the front legs 63a and the rear legs 64b of the first chair 61a located on the upper side are surely grounded, and therefore, two chairs, if combined, are not loose as one chair and can be comfortably used. 
     FIGS. 28A to 29B show the seventh embodiment of the present invention. 
     A combination chair of the present invention consists of a first chair 71a and a second chair 71b. Seat portions 72a and 72b of the chairs 71a and 71b are made of rectangular boards having substantially the same size. 
     Mid portions of a pair of the front legs 73a is fixedly jointed to the front end locations of both sides of the seat portion 72a of the first chair 71a. The upper end portions of the front legs 73a are formed into armrests 74 which are bent towards the rear side substantially in an L-shape, and the rear end portions of a pair of the armrests 74 are formed into a backrest 75a arranged along with the width direction of the seat portion 72a. A back plate 76a is formed in such a manner that the upper and lower ends thereof are fixed to the mid portion of the backrest 75a and the rear end surface of the seat portion 72a, respectively. That is, the front legs 73a, the armrests 74 and the backrest 75a are integrally formed of one rod member made of metal or wood. 
     On both sides of the rear end portion of the seat portion 72a, the mid portions of rear legs 77a made of substantially straight rod members are fixed. The upper ends of the rear legs 77a are jointed to the lower surfaces of the rear portions of the armrests 74. 
     The front legs 73b are provided downward from the two corners of the front-end side of the lower surface of the seat portion 72b of the second chair 71, and the mid portions of the rear legs 77b are fixed to both ends of the rear end portion of the seat portion. 
     The upper ends of the pair of the rear legs 77b are connected to each other, and formed into the backrest 75b bent towards the rear side in an L-shape, and a backrest 76b is formed in such a manner that the upper and lower ends thereof are fixed to the mid portion of the backrest 75b and the rear end surface of the seat portion 72b. The mid portions of the front legs 73b and the rear legs 77b are connected via a reinforcing rod 78 having a square bracket shape (]) to each other for three sides excluding the rear side of the seat portion 72b. 
     The seat portion 72b of the second chair 71b is set at such a height that the upper surface thereof is brought into contact with the lower surface of the seat portion 72a of the first chair 71a. The lengths of the front legs 73a and the rear legs 77a of the first chair 71a are determined so that they are grounded on the floor when the first chair 71a is stacked upon the second chair 71b. 
     When the first chair 71a is stacked upon the second chair 71b, the measurements in terms of the front-rear direction are determined so that the backrest 75b of the second chair 71b is fitted to the lower surface side of the backrest 75a of the first chair 71a, and the back plate 76b of the second chair 71b is fitted to the back surface of the back plate 76a of the first chair 71a. The distance between legs and the positions thereof in terms of the front-rear direction are determined so that the pair of the front legs 73b of the second chair 71b are fitted between the inner sides, in terms of the width direction, of the pair of the front legs 73a of the first chair 71a, and the rear legs 77b are fitted to the back portions of the rear legs 77b of the first chair 71a. 
     According to the combination chair having the above-described structure, the first chair 71a and the second chair 71b are stacked up together, and can be used as one chair. 
     When the first and second chairs 71a and 71b are combined together, the backrest 75b of the second chair 71b is fitted to the lower surface side of the backrest 75a of the first chair 71a, thus exhibiting an appearance as if they are one backrest. 
     Further, when the two chairs are combined, the pair of the front legs 73 of the second chair 71b are fitted on the inner sides of the pair of the front legs 73a of the first chair 71a, thus suppressing the shaky movement of the chairs in the right-to-left direction, and the backrests 75a and 75b are fitted with each other in the up-and-down direction, thus suppressing the shaky movement in the up-and-down movement. Furthermore, the rear legs 77a and 77b, and the backrests 76a and 76b are fitted in terms of the front-rear direction, thus suppressing the shaky movement in the front-rear direction. 
     With the above structure, if the two chairs are used as one chair, they can be used comfortably without looseness. 
     ADVANTAGE OF THE INVENTION 
     As described above, the present invention has the structure in which a plurality of chairs each having a seat portion supported by legs and a backrest provided on the seat portion, can be stacked up together, without looseness or having a shaky movement. 
     With the plurality of chairs, the number of chairs can be increased or decreased in accordance with an increase or decrease in the number of users. A plurality of chairs are stacked up when the number of chairs is decreased, and therefore an extra space is not necessary. 
     Further, the plurality of chairs stacked up are prevented from being loose, and they do not shakily move. Therefore, the chairs, if they are combined, can be easily used.