the embodiments of the image display apparatus of the present invention are explained below with reference to the drawings . fig1 shows the external view of an image display apparatus 1 of a first embodiment . the image display apparatus 1 comprises a display unit 10 , a pair of left and right prisms 20 l and 20 r , a nose pad assembly 31 , and a pair of left and right temples 32 l and 32 r , and is worn in front of the face of a user such that the prisms 20 l and 20 r are located in front of the left and right eyes , respectively . the nose pad assembly 31 is mounted to the prisms 20 l and 20 r and connect them . the temples 32 l and 32 r are mounted to the end areas of the prisms 20 l and 20 r , respectively . when the apparatus is worn , the nose pad assembly 31 rests on the nose , and the temples 32 l and 32 r rest on the ears , the sides of the head , or the rear area of the head , such that the image display apparatus 1 is supported by these three members . the temples 32 l and 32 r may be rotated around vertical axes ( not shown in the drawing ) located near the prisms 20 l and 20 r , respectively , such that they may be folded inward during non - use . the display unit 10 is mounted to the right prism 20 r . fig2 shows the cross - section thereof including the display unit 10 . the display unit 10 comprises a transmission - type liquid crystal display device ( lcd ) 11 , a container 12 , a prism 13 , a light emitting diode ( led ) 14 , and a lens 15 . the lcd 11 displays an image to be provided to the user and the illuminating light is modulated by the displayed image the container 12 houses and supports the lcd 11 , the led 14 , and the lens 15 . the led 14 is a light source to illuminate the lcd 11 , and the lens 15 is an illuminating optical system to lead in a uniform fashion the light emitted by the led 14 to the entire surface of the lcd 11 . the image displayed by the lcd 11 and the light emitted by the led 14 are controlled by a controller ( not shown in the drawings ) located outside the image display apparatus 1 . the controller is connected to the container 12 by a cable 40 , as shown in fig1 and supplies power and image signals through the cable 40 . the prism 13 has a flat plate configuration , and is made of clear glass or resin . the prism 13 leads light from the lcd 11 to the eye e of the user , and provides a virtual image of the image displayed on the lcd 11 . the upper end area of the prism 13 has a wedge configuration in which the end area is thicker than the inner side , and the container 12 is mounted to the prism 13 such that it sandwiches the wedge - shaped upper end area . the prism 20 l has a flat plate configuration and comprises a single member . the prism 20 r also has a flat plate configuration , but comprises the prism 13 and a prism 21 , instead of just a single member . the prisms 20 l and 21 are made of the same material as the prism 13 , and there is no difference in the index of refraction among these three prisms . the prisms 13 and 21 that comprise the prism 20 r have mutually compensating configurations and are glued together such that they have no substantial gap in between and their surfaces are contiguous . except for a wedge - shaped upper end area of the prism 13 , the prisms 20 l and 20 r are symmetrical . the user wearing the image display apparatus 1 in front of his or her face observes the external world through the prisms 20 l and 20 r . the lower end area of the prism 13 is constructed such that it has a wedge configuration wherein the front surface ( the surface farther away from the eye e ) approaches the rear surface ( the surface closer to the eye e ) toward the lower end . the front surface of this wedge - shaped part , i . e ., the surface that connects to the prism 21 , is a flat surface , and a hologram element 22 is formed on this surface . the hologram element 22 becomes located immediately in front of the eye e when the apparatus is worn . the prism 13 and the hologram element 22 comprise an eyepiece optical system 16 . the prism 13 leads light located in the interior thereof from the lcd 11 via an end surface of the upper end area of the prism 13 to the hologram element 22 while conducting total reflection via the front and rear surfaces of the prism 13 several times . the hologram element 22 diffracts the thus led light , converts it to essentially parallel light , and causes it to strike the eye e . as a result , a virtual image of the image displayed on the lcd 11 is provided to the user . the hologram element 22 operates only minimally on external light , so that the virtual image is observed to be superimposed over the center of external images . the hologram element 22 is designed such that the distance from the eye e to the virtual image will appear to be one to three meters and the size of the virtual image will appear to be several times to several tens of times larger than the real image displayed on the lcd 11 . therefore , the image provided to the user is easy to observe . the user can clearly observe the displayed image and external images through a simple slight adjustment of the focal point of the eye e . in the image display apparatus 1 , light from the lcd 11 is led to the hologram element 22 while it is reflected inside the prism 13 , and therefore the prism 20 r may be made large in size . as a result , the container 12 may be located around or outside the field of view of the eye e , minimizing the range of the field of view blocked by the container 12 . in addition , because most of the external light passes through the prism 20 r and strikes the eye e , image distortion or color bleeding does not occur in the external images except for extreme edge areas . moreover , since the width of the prism 20 r may be made small , around three millimeters for example , the entire apparatus becomes lightweight . the lower end area of the prism 13 has a wedge configuration , but because it is connected to the prism 21 , which is made of the same material as the prism 13 , no refraction occurs with regard to the external light that passes through the lower end area of the prism 13 . therefore , the center area of the external images does not experience distortion or discontinuity , and the image display apparatus 1 can provide high quality images . the lcd 11 has a rectangular configuration that is horizontally long , and is capable of displaying one to several lines of character strings comprising less than 20 characters aligned horizontally . consequently , the user can obtain a large amount of information from the displayed image at once . the container 12 is designed such that its length a that extends in the direction that connects the eye e and the container 12 is approximately twice as long as the length b that extends in the direction perpendicular to the above direction and the horizontal direction . therefore , the container 12 is thin and the range of the field of view blocked by the container 12 is small . the lcd 11 is located such that its display surface becomes perpendicular to a straight line that connects the eye e and the center of the display surface thereof , and the lens 15 and led 14 are located along a line extending from the above straight line . based on this construction , while the container 12 is thin , the lcd 11 , the lens 15 , and the led 14 may be easily arranged inside of it , and an illuminating optical system may be constructed in a simple fashion using the lens 15 only . [ 0044 ] fig3 shows an example of the field of view of the eye e and the range of the field of view blocked by the container 12 . this example shows a case in which the entire container 12 is located within a field of view v 0 . the range of the field of view v 1 , which is a portion of the field of view v 0 blocked by the container 12 , is small . as described above , it is also possible to locate a part of the container 12 outside the field of view v 0 , so that is possible to further reduce the range of field of view blocked by the container 12 . the container 12 has a configuration such that an angle α over which the field of view is blocked is determined only by a part of the container that is closer to the eye e than the center thereof in terms of a direction connecting the eye e and the container 12 . because the container 12 is thin , the range of field of view blocked by the container 12 is small ; thus , this configuration enables the range of the blocked field of view to be further reduced and the container 12 to be made lightweight . if the angle over which the field of view is blocked were to be determined by a part of the container closer to the eye e than the above center and a part of the container farther away from the eye e than the above center , even if the container has a similar configuration , the range of the blocked field of view would increase . if the angle over which the field of view is blocked were to be determined only by a part of the container farther away from the eye e than the above center , the container 12 would increase in size and weight . in this embodiment , the displayed image is provided to the right eye , but naturally it is acceptable if the displayed image is provided to the left eye instead . [ 0047 ] fig4 shows the external view of an image display apparatus 2 of a second embodiment . the image display apparatus 2 comprises the above image display device 1 plus a frame 50 , such that the container 12 , the prisms 20 l and 20 r , the nose pad assembly 31 and the temples 32 l and 32 r are mounted to the frame 50 . while the width ( the horizontal length ) of the prism 13 was approximately one - third that of the prism 21 in the image display apparatus 1 , in the image display apparatus 2 , the width of the prism 13 is the same as the width of the prism 21 . using this construction , while the range of the blocked field of view increases due to the existence of the frame 50 , a wide image may be provided . the configuration of the container 12 and the constructions and functions of the prism 13 and hologram element 22 comprising an eyepiece optical system 16 , and of the prism 21 , are the same as in the image display apparatus 1 , as shown in the cross - sectional view of fig5 . the cable 40 that connects the apparatus with the controller is attached to the rear end of the temple 32 l , and is connected to the container 12 through the inside of the temple 32 l and the frame 50 . [ 0049 ] fig6 shows an external view of an image display apparatus 3 of a third embodiment . the image display apparatus 3 includes a pair of display units 10 l and 10 r such that an image may be provided to both eyes , and includes prisms 20 l and 20 r provided with magnification powers such that the apparatus can correct the vision of the user . the construction of each of the display units 10 l and 10 r is the same as the construction of the display unit 10 of the image display apparatus 1 of the first embodiment , except that the prisms 13 l and 13 r are curved . the container 12 r is connected to the controller via the cable 40 , and the container 12 l is connected to the controller via the cable 40 a , the container 12 r and the cable 40 . the magnification powers of the prisms 20 l and 20 r are set in accordance with the vision of the user . by providing the prisms 20 l and 20 r with negative magnification powers , the apparatus can correct nearsightedness , and by providing them with positive magnification powers , the apparatus can correct farsightedness . the lower end surfaces of the prisms 13 l and 13 r that connect with the prisms 21 l and 21 r , respectively , are flat surfaces , so that hologram elements 22 l and 22 r may be easily formed thereon . in the image display apparatus of an embodiment that includes one or two display units each including a display device that displays images , a container that supports the display device , and an eyepiece optical system that leads the light from the display device to the eye and provides a virtual image of the displayed image , wherein at least one length of the container that extends in the direction perpendicular to the direction connecting the container and the eye is smaller than the length of the container that extends in the direction connecting the container and the eye , the container may be made small , so that the range of field of view blocked by the container is small . therefore , a highly safe apparatus may be obtained . in addition , a light source and optical system to illuminate the display device may be easily incorporated in the container . where the container supports the display device such that the display surface thereof is essentially perpendicular to the direction that connects the center of the display surface and the eye , even if a simple and relatively inexpensive transmission - type display device is used , the illuminating light source and optical system may be arranged with few limitations , and the container may be reliably made thin . moreover , because the illuminating light source and optical system can be simple and lightweight in construction , the resulting apparatus may be small , lightweight and comfortable to use . in the image display apparatus of the present invention that includes one or two display units including a display device that displays images , a container that supports the display device , and an eyepiece optical system that leads light from the display device to the eye and provides a virtual image of the displayed image , wherein the container has a configuration such that the angle over which the field of view is blocked is determined only by a part of the container closer than the center thereof to the eye in the direction connecting the container and the eye , the field of view blocked by the container is small , resulting in a highly safe apparatus as well . where the apparatus includes a prism that allows external light to pass through and leads it to the eye , and part of the prism operates as an eyepiece optical system and leads light from the display device to the eye , the occurrence of distortion and discontinuity in the external images caused by the eyepiece optical system may be avoided , and the user feels no discomfort . moreover , because the container , nose pads , and temples may be mounted to the prism , a connecting member such as a frame used to integrate these members is no longer necessary , and the range of the blocked field of view may be further reduced . in the image display apparatus of an embodiment that includes one or two display units including a display device that displays images , a container that supports the display device , and an eyepiece optical system that leads light from the display device to the eye and provides a virtual image of the displayed image , and a pair of prisms that are located in front of the eyes allow external light to pass through and lead it to the left and right eyes , wherein the prisms are mounted to the nose pad assembly and the temples and the container or containers are mounted to the prisms , a connecting member such as a frame used to integrate the container or containers , nose pad assembly and temples is not needed . therefore , the field of view is not blocked by a connecting member , resulting in a highly safe apparatus . in addition , the apparatus becomes lightweight and is comfortable to use . because a part of each prism works as an eyepiece optical system and leads light from the display device to the eye , the occurrence of distortion and discontinuity in external images due to the effect of the eyepiece optical system may be avoided in this apparatus as well , and natural images may be provided to the user . where the container is mounted around the prism , and the prism has surfaces which include a surface that leads light from the display device to the interior thereof , a surface that reflects several times inside the prism the light thus led to the interior thereof and leads it close to the eye , and a surface that directs the light thus led to a location immediately in front of the eye , and these surfaces comprise an eyepiece optical system , the container may be located around or outside the field of view , resulting in a larger field of view and higher safety . moreover , the prism may be made thin , resulting in a lightweight apparatus . where the surface that directs toward the eye the light led to a location immediately in front of the eye comprises a hologram element , both the light from the display device and the external light may be led to the eye without light loss , so that all of the displayed image and external images may be viewed with sufficient brightness . in addition , the construction is simple and easy to manufacture . where the prisms are given magnification powers to correct the diopter , the apparatus can function as vision - correcting glasses , and a user with weak vision can clearly observe the external world . although the present invention has been fully described by way of example with reference to the accompanying drawings , it is understood that various changes and modifications will be apparent to those skilled in the art . therefore , unless such changes and modifications depart from the scope of the present invention , they should be construed as being included therein .