now preferred embodiment of the present invention will be explained referring to the attached drawings . fig1 is a partially cutaway front view showing a diagrammatical construction of the magnetizing apparatus of the present invention . fig2 is a perspective view of an essential part of the apparatus of fig1 . fig3 is an enlarged view of the area “ x ” of fig1 . fig4 - fig9 are an enlarged view of the area “ x ” according to other embodiments , respectively . fig1 is a partially cutaway perspective view of an essential part of a modified embodiment shown in fig1 - fig1 . in the magnetizing apparatus a shown in fig1 - fig3 , a fixture 2 is mounted on a rotary spindle apparatus 1 so as to be rotatable around an axis l . the reference numeral 1 a is a rotary drive motor of the spindle apparatus 1 . the fixture 2 is comprised of a jaw type chuck means and three chuck jaws 2 b . . . of sector form ( 120 degrees ) made of non - magnetic material are provided on a base 2 a so as to be movable in radial direction . in the figure when the chuck jaws 2 b . . . are moved in centrifugal direction , they are tightly held in an inner tubular part of a tubular member ( work ) to hold and fix the work . although it is not shown in the figure , it goes without saying that an automatic or manual operation means for adjusting the movement of the jaw chucks 2 b . . . in radial direction is provided for the base 2 a . the chuck jaws 2 b . . . may be prepared corresponding to the size of work and detachable and exchangeable by means of a fixture ( not shown ) from the base 2 a . a ring reinforcement 3 is formed by sheet metal work of a magnetic metal like a stainless steel and is comprised of a tubular part 3 a and an outward flange portion 3 b ( two parts , namely a tubular part and an other part integrally formed with the tubular part ). the annular object to be magnetized 4 is made of a rubber material like fkm , nbr , h - nbr , epdm , cr , acm , aem , vmq , or fvmq in which magnetic powder like ferrite is mixed . the object 4 is integrally attached on the outer surface and outer circumference of the outward flange portion 3 b by means of vulcanization . the ring reinforcement 3 integrally attached with the annular body to be magnetized 4 is used as a work and the tubular part 3 a thereof is held and fixed by the fixture 2 . a magnetizing yoke 5 is constructed such that a coil 5 b is wound around a ring breakage iron core 5 a like the letter c and electric current is supplied to the coil 5 b to generate a magnetic field from the ring breakage iron cores 51 , 52 . the magnetizing yoke 5 is provided near the fixture 2 . a pressing means 5 c is provided behind the magnetizing yoke 5 so as to slightly press the ring breakage iron core 52 onto the outer circumference of the tubular part 3 a by means of a spring . a magnetizing method of the magnetizing apparatus a will be explained . the ring reinforcement 3 is formed by metal sheet work of a magnetic material , the rubber material mentioned above is attached on the outer surface ( flat surface ) and peripheral edge of the outward flange portion 3 b to be integrated , thus forming the annular body to be magnetized 4 . the ring reinforcement 3 integrated with the annular body to be magnetized 4 is held and fixed with the tubular part 3 a by means of chuck jaws 2 b . . . of the fixture 2 . the magnetizing yoke 5 is provided near the fixture 2 in such a manner that the ring breakage end 52 ( the other end ) of the magnetizing yoke 5 is pushed so as to slightly get in touch with the outer circumference of the tubular part 3 a by means of the pressing means 5 c and another ring breakage end 51 ( one end ) thereof is approached into the surface of the annular body to be magnetized 4 . a motor 1 a of the rotary spindle apparatus 1 is driven to rotate the fixture 2 around the axis l and electric current is applied to the coil 5 b wound around the magnetizing yoke 5 . application of electric current is controlled based on a control sequence which is programmed to alternately reverse current direction , i . e . change current toward a positive or negative direction at a short predetermined interval . as a result , a circular closed loop of a magnetic flux “ a ” is generated , the flux passing the ring breakage end 51 - the annular body to be magnetized 4 - the ring reinforcement 3 - the ring breakage end 52 and returning to the ring breakage 51 . the direction of the magnetic flux “ a ” is changed depending on an alternate application of the electric current , thereby alternately changing the passing direction of the flux at a short interval as shown at the arrows in fig3 . during such application of alternate magnetic flux , the annular body to be magnetized 4 rotates around the axis l , so that the magnetic powder contained in the annular body is magnetized in a manner that s poles and n poles are alternately appeared along its periphery of the annular body , thereby making a multi - pole magnetized tone wheel . the fixture 2 is made of non - magnetic body , therefore , the magnetic flux “ a ” does not leak into the fixture 2 , the density of magnetic flux “ a ” in the circular closed loop is kept constant , and the magnetizing pattern formed on the annular body to be magnetized 4 becomes constant along the circumferential direction , thereby obtaining a tone wheel of good quality . the fixture 2 is comprised of a jaw type chuck means , however , the space between the jaws does not affect magnetizing , so that a general purpose jaw type chuck means is used as a fixture , thereby obtaining wide design freedom . further , the positioning of the magnetizing yoke 5 is executed by slightly pressing the ring breakage end 52 into the outer circumference of the tubular part 3 a by means of the pressing means 5 c , thereby contributing accuracy and facilitation . the embodiment shown in fig4 explains a magnetizing method in which a ring reinforcement 3 is made of a tubular part 3 a and an inward flange portion 3 c integrally formed with the tubular part 3 a ( two parts , namely a tubular part and an other part integrally formed with the tubular part ) and the annular body to be magnetized 4 is integrally attached to the outer circumference of the tubular part 3 a . in this embodiment , like the above - mentioned embodiment 1 , the tubular part 3 a of the ring enforcement 3 is held and fixed with the fixture 2 . however , in this embodiment , the inward flange portion 3 c is positioned on the fixture 2 while they are fixed . the pressing means 5 c is provided on the magnetizing yoke 5 . the magnetizing yoke 5 is provided in such a manner that the ring breakage end 52 ( the other end ) is pushed onto the upper face of the inward flange portion 3 c by means of the pressing means 5 c and the ring open end 51 ( one end ) is approached to the outer circumference of the tubular part 3 a to which the annular body to be magnetized 4 is integrally attached . after the above - mentioned preparation , an alternate electric current is applied to the coil 5 b while rotating the fixture 2 around the axis l as mentioned above , a circular closed loop of the magnetic flux “ a ” is generated along the ring breakage end 51 - the annular body to be magnetized 4 - the ring reinforcement 3 - the ring breakage end 52 - the ring breakage end 51 . the magnetizing pattern is formed on the annular body to be magnetized 4 in a manner that s poles and n poles are alternately repeated around the its periphery . also in this embodiment , the fixture 2 is made of non - magnetic body , therefore , the magnetic flux “ a ” does not leak into the fixture 2 , the density of magnetic flux “ a ” in the circular closed loop is kept constant , and the magnetizing pattern formed on the annular body to be magnetized 4 becomes constant along the circumferential direction , thereby obtaining a tone wheel of good quality . the fixture 2 is comprised of a jaw type chuck means , however , the space between the jaws does not affect magnetizing , so that a general purpose jaw type chuck means is used as a fixture , thereby obtaining wide design freedom , like the above - mentioned embodiment . other constructions and effects are the same as those of the above - mentioned embodiment , so that the common members have the same reference numerals and their explanations are omitted here . the pressing means 5 c may not be provided in the embodiments 1 , 2 and the ring breakage end 52 of the magnetizing yoke 5 may be provided near the ring reinforcement 3 . the embodiment shown in fig5 shows a magnetizing method in which a ring reinforcement 3 is comprised of a thick tubular part 3 a and an end face 3 b corresponding to the thickness ( two parts , namely a tubular part and an other part integrally formed with the tubular part ) and the annular body to be magnetized 4 is integrally attached with the outer circumference of the tubular part 3 a . the magnetizing yoke 5 is constructed such that the coil 5 b is wound at three parts of an iron core 5 a like the letter e , two ends 52 ( other end ) are attached or approached to the upper and lower end faces 3 d of the ring enforcement 3 respectively , and another end 51 ( one end ) is approached to the outer circumference of the tubular part 3 a to which the annular body to be magnetized 4 is integrally attached . as mentioned above , an alternate electric current is applied to the coil 5 b while rotating the fixture 2 around the axis l as mentioned above , a circular closed loop of the magnetic flux “ a ” is generated along the ring breakage end 51 - the annular body to be magnetized 4 - the ring reinforcement 3 - the ring breakage end 52 - the ring breakage end 51 . in this case , the magnetic flux path is divided into two directions from the ring breakage end 51 and two circular closed loops of the magnetic flux “ a ” are formed . the magnetizing pattern is also formed on the annular body to be magnetized 4 in a manner that s poles and n poles are alternately repeated around the circumferential direction . also in this embodiment , the fixture 2 is made of non - magnetic body , therefore , the magnetic flux “ a ” does not leak into the fixture 2 , the density of magnetic flux “ a ” in the circular closed loop is kept constant , and the magnetizing pattern formed on the annular body to be magnetized 4 becomes constant along the circumferential direction , thereby obtaining a tone wheel of good quality . the fixture 2 is comprised of a jaw type chuck means , however , the space between the jaws does not affect magnetizing , so that a general purpose jaw type chuck means is used as a fixture , thereby obtaining wide design freedom . other constructions and effects are the same as those of the above - mentioned embodiments , so that the common members have the same reference numerals and their explanations are omitted here . the embodiment shown in fig6 explains a magnetizing method in which the ring reinforcement 3 is comprised of the tubular part 3 a and a plane annular part 3 e which is formed by sheet metal processing so as to bend a part of the tubular part 3 a to be folded ( two parts , namely a tubular part and an other part integrally formed with the tubular part ) and the annular body to be magnetized 4 is integrally attached on the plane annular part 3 e . in this embodiment , the tubular part 3 a of the ring reinforcement 3 is held and fixed to the fixture 2 like the above - mentioned embodiments , however , there is a space 2 c formed by the smaller diameter part of the fixture 2 in the back of the tubular part 3 a . the magnetizing yoke 5 is positioned in such a manner that the ring breakage end 51 ( one end ) of the magnetizing yoke 5 like the letter c is approached to the annular body to be magnetized 4 and the ring breakage end 52 ( the other end ) is positioned apart from the ring reinforcement 3 . the apart position is outside of the outer circumference “ b ” of the annular body to be magnetized 4 attached on the plane annular part 3 e and is near the ring reinforcement 3 from the upper face position “ c ” of the annular body to be magnetized 4 . in this case , the ring breakage end 52 ( the other end ) is preferably positioned near the ring reinforcement 3 from the back face position “ d ” of the annular body to be magnetized 4 . therefore , the magnetic circular closed loop penetrating the annular body to be magnetized 4 is efficiently formed and a tone wheel with superior magnetic characteristic is obtained . as mentioned above , an alternate electric current is applied to the coil 5 b while rotating the fixture 2 around the axis l as mentioned above , a circular closed loop of the magnetic flux “ a ” is generated along the ring breakage end 51 - the annular body to be magnetized 4 - the ring reinforcement 3 - the ring breakage end 52 - the ring breakage end 51 . in this case the ring breakage end 52 is apart from the ring reinforcement 3 , however , the members other than the magnetizing yoke 5 , the ring reinforcement 3 and the annular body to be magnetized 4 are made of non - magnetic material , so that there is no other space to form a circular closed loop of the magnetic flux and the same magnetizing as mentioned above is executed by the circular closed loop of the magnetic flux “ a ” as shown in the figure . the space 2 c is formed in the back of the tubular part 3 a and directivity of magnetic flux into the fixture 2 is weakened , thereby effectively forming a circular closed loop of the magnetic flux “ a ”. other constructions and effects are the same as those of the above - mentioned embodiments , so that the common members have the same reference numerals and their explanations are omitted here . in this case , even if the ring reinforcement 3 is made of non - magnetic material , the circular closed loop of the magnetic flux “ a ” as shown in the figure is formed . the embodiment shown in fig7 explains a modified embodiment of the magnetizing method by means of the ring enforcement 3 and the annular body to be magnetized 4 attached to the outward flange portion 3 b as explained in the embodiment 1 . as mentioned above , a circular closed loop of the magnetic flux “ a ” is generated along the ring breakage end 51 - the annular body to be magnetized 4 - the ring reinforcement 3 - the ring breakage end 52 - the ring breakage end 51 . in this case , the ring breakage end 52 is apart from the ring reinforcement 3 like the embodiment 4 , however , the members other than the magnetizing yoke 5 , the ring reinforcement 3 and the annular body to be magnetized 4 are made of non - magnetic material , so that there is no other space to form a circular closed loop of the magnetic flux and the same magnetizing as mentioned above is executed by the circular closed loop of the magnetic flux “ a ” as shown in the figure . the positioning of the ring breakage end 52 , the outer circumference “ b ” of the annular body to be magnetized 4 , the upper face position “ c ” of the annular body to be magnetized 4 , and the back face position “ d ” of the annular body to be magnetized 4 is preferably the same as that in the embodiment 4 . like the embodiment 2 the embodiment shown in fig8 explains a magnetizing method in which the ring reinforcement 3 is made of the tubular part 3 a and the inward flange portion 3 c integrally formed with the tubular part 3 a ( two parts , namely a tubular part and an other part integrally formed with the tubular part ) and the annular body to be magnetized 4 is integrally attached to the outer circumference ( plane face ) of the inward flange portion 3 c . also in this embodiment , the circular closed loop of the magnetic flux “ a ” is formed along the ring breakage end 51 - the annular body to be magnetized 4 - the ring reinforcement 3 - the ring breakage end 52 - the ring breakage end 51 . in the embodiment shown in fig9 , the ring reinforcement 3 is made of the tubular part 3 a and the outward flange portion 3 c integrally formed with the tubular part 3 a ( two parts , namely a tubular part and an other part integrally formed with the tubular part ) like the embodiment 1 , however , the outer circumference of the tubular part 3 a is held and fixed with the fixture 2 . namely , the chuck jaws 2 b of the fixture 2 externally hold the tubular part 3 a by being moved into centripetal direction . the annular body to be magnetized 4 is integrally attached to the outer circumference ( plane face ) of the outward flange portion 3 b . also in this embodiment , the circular closed loop of the magnetic flux “ a ” is formed along the ring breakage end 51 - the annular body to be magnetized 4 - the ring reinforcement 3 - the ring breakage end 52 - the ring breakage end 51 . other constructions and effects in the embodiments 5 - 7 are the same as those of the above - mentioned embodiments , so that the common members have the same reference numerals and their explanations are omitted here . fig1 shows an embodiment in which a ring - like positioning table 6 for positioning the annular body to be magnetized 4 attached to the ring reinforcement 3 made of magnetic material prior to applying alternate magnetic flux is interposed between the ring reinforcement 3 and the other end 52 of the magnetizing yoke 5 in the embodiment 4 . the positioning table 6 is provided around the fixture 2 so as to be upwardly energized on a positioning base 60 by means of a compression spring 6 a . the positioning table 6 is provided for positioning the annular body to be magnetized 4 at a fixed position . in a pre - process of magnetizing , the ring reinforcement 3 made of magnetic material attached with the annular body to be magnetized 4 is placed on the positioning table 6 as shown in the figure , a positioning base plate ( not shown ) is pressed onto the upper surface of the annular body to be magnetized 4 resisting the elasticity of compression spring 6 a from above to keep the body 4 at a fixed position . under such condition , the chuck jaws 2 b . . . of the fixture 2 are operated to fix the ring reinforcement 3 to the fixture 2 by means of the tubular part 3 a . then , the positioning base plate is retracted and the same magnetizing as mentioned above is executed while rotating the fixture 2 . the positioning table 6 is preferably designed to be retracted into other position after completing the above - mentioned positioning . however , such design makes the apparatus complicated , so that the plate 6 is integrally or separately provided around the fixture 2 in general and is interposed between the ring reinforcement 3 made of magnetic material and the other end 52 of the magnetizing yoke 5 . when the annular body to be magnetized 4 is magnetized with the magnetizing yoke 5 while rotating the fixture 2 , a circular closed loop of a magnetic flux “ a ” is formed along the ring breakage end 51 - the annular body to be magnetized 4 - the ring reinforcement 3 - the positioning table 6 - the ring breakage end 52 as shown in the figure . when the positioning table 6 is made of magnetic material , a magnetic circular closed loop is effectively formed . however , when the plate 6 is positioned as shown in the figure , even if it is made of non - magnetic material , the forming efficiency of magnetic circular closed loop is not reduced so much . that is , when the positioning table 6 made of magnetic material is interposed between the ring reinforcement 3 made of magnetic material and the other end 52 of the magnetizing yoke 5 , the alternate magnetic flux “ a ” forms the circular closed loop shown with the solid lines along the shape of the positioning table 6 . when the positioning table 6 is made of non - magnetic material , the magnetic flux “ a ′” with the two - dotted lines in the figure is formed so as to connect the shortest distance of the ring reinforcement 3 made of magnetic material and the other end 52 of the magnetizing yoke 5 . as the result , an alternate magnetic flux “ a ” forms a circular closed loop along the one end 51 of the magnetizing yoke - the annular body to be magnetized 4 - the ring reinforcement 3 - the positioning table 6 - the other end 52 of the magnetizing yoke as shown in the figure . if the positioning table 6 is integrated with the fixture 2 , they are rotated together . if the positioning table 6 is provided separately , it stands still while the fixture 2 is rotated . the positioning of the ring breakage end 52 , the outer circumference “ b ” of the annular body to be magnetized 4 , the upper face position “ c ” of the annular body to be magnetized 4 , and the back face position “ d ” of the annular body to be magnetized 4 is preferably the same as that in the embodiment 4 . other constructions are the same as those of the above - mentioned embodiments , so that the common members have the same reference numerals and their explanations are omitted here . fig1 shows an embodiment in which the ring - like positioning table 6 for positioning the annular body to be magnetized 4 attached to the ring reinforcement 3 made of magnetic material , prior to applying an alternate magnetic flux , is interposed between the ring reinforcement 3 made of magnetic body and the other end 52 of the magnetizing yoke 5 in the embodiment 5 . when the positioning table 6 is made of magnetic material or a non - magnetic material , an alternate magnetic flux forms a circular closed loop along the one end 51 of the magnetizing yoke - the annular body to be magnetized 4 - the ring reinforcement 3 - the positioning table 6 - the other end 52 of the magnetizing yoke ( if the positioning table 6 is made of non - magnetic material , along the magnetic flux “ a ′” shown with two - dotted lines like the above - mentioned embodiment ). other constructions are the same as those of the embodiment 8 , so that the common members have the same reference numerals and their explanations are omitted here . fig1 shows an embodiment in which the ring reinforcement 3 is made of the tubular part 3 a and the inward flange portion 3 c integrally formed with the tubular part 3 a ( two parts , namely a tubular part and an other part integrally formed with the tubular part ), the annular body to be magnetized 4 is integrally attached to the outer circumference ( plane face ) of the inward flange portion 3 c , the outer circumference of the tubular part 3 a is held with the chuck jaws 2 b . . . like the embodiment 7 , the ring - like positioning table 6 for positioning the annular body to be magnetized 4 attached to the ring reinforcement 3 made of magnetic material , prior to applying an alternate magnetic flux , is interposed between the ring reinforcement 3 and the other end 52 of the magnetizing yoke 5 . in this embodiment , the positioning table 6 is upwardly energized on the base 2 a of the fixture 2 via the compression spring 6 a in the chuck jaws 2 b . . . and is rotated together with the fixture 2 around the axis l . also in this embodiment , if the positioning table 6 is made of magnetic material or a non - magnetic material , the alternate magnetic flux forms a circular closed loop along the one end 51 of the magnetizing yoke - the annular body to be magnetized 4 - the ring reinforcement 3 - the positioning table 6 - the other end 52 of the magnetizing yoke ( if the positioning table 6 is made of non - magnetic material , along the magnetic flux “ a ” shown with two - dotted lines like the above - mentioned embodiment ). other constructions are the same as those of the embodiment 8 , so that the common members have the same reference numerals and their explanations are omitted here . fig1 shows a modified embodiment in which the ring - like positioning table 6 is interposed between the ring reinforcement 3 made of magnetic body and the other end 52 of the magnetizing yoke 5 . when the positioning table 6 is made of magnetic body and is fixedly provided ( not rotated ), gaps 6 c , 6 c are provided by cutting both sides of the positioning table 6 corresponding to the position of the magnetizing yoke 5 , and a screen - like part 6 b between the gaps 6 c , 6 c is formed as a part of the ring - like positioning table 6 intervened between the ring reinforcement 3 and the other end 52 of the magnetizing yoke 5 . in case of magnetizing , an alternate magnetic flux forms a circular closed loop along the one end 51 of the magnetizing yoke - the annular body to be magnetized 4 - the ring reinforcement 3 made of magnetic material - the part 6 b of the positioning table 6 - the other end 52 of the magnetizing yoke . in this case , leak of the magnetic flux is reduced because of the gaps 6 c , 6 c and the narrow part 6 b of the positioning table 6 is formed as a magnetic flux path , thereby enlarging the magnetic flux density and forming a efficient magnetic circular closed loop . the ring reinforcement 3 in this embodiment is made of the tubular part 3 a and the outward flange portion 3 c integrally formed with the tubular part 3 a ( two parts , namely a tubular part and an other part integrally formed with the tubular part ) and the annular body to be magnetized 4 is integrally attached to the outer circumference ( plane face ) of the outward flange portion 3 b . although , the positioning pattern by the positioning table 6 and the holding and fixing pattern by the fixture 2 are similar to those in the embodiment 9 , this embodiment can be applied to the positioning patterns with other ring reinforcement 3 , annular body to be magnetized 4 , and positioning table 6 and the holding and fixing pattern with other fixture 2 . the ring reinforcement 3 integrated with thus magnetized tone wheel is provided for the rotating member of the bearing system as a slinger and a combination seal ring of the bearing can be assembled . a magnetic sensor is provided for the fixing member so as to oppose the tone wheel , thus simply constructing a magnetic encoder for detecting the rotational velocity . the magnetizing pattern formed on the tone wheel is uniform and has high magnetizing accuracy in the circumferential direction , so that thus formed magnetic encoder has a large vocation for detecting the rotational velocity of automobile wheels . the mechanism of the jaw type chuck means of the fixture 2 is not limited to those shown in the figures , and it goes without saying that other kinds of generally used chuck means can be used . it is possible to further provide a speed accelerator / reducer for the motor 1 a of the rotary spindle apparatus 1 to change the formation interval of the s poles and n poles by varying the rotational speed of the fixture . or it may be possible to provide a magnetizing power source for the s poles and the n poles respectively or to control the magnetizing power source output to vary the magnetizing strength depending on the purpose , associating with the output of the magnetizing yoke 5 . in this case , the magnetizing current direction is switched ( reversed ) per a desired angle displacement by the signal from the encoder ( not shown ) provided for the spindle apparatus 1 during magnetizing . thus varying a desired angle , the interval of magnetized s poles and n poles can be optionally changed . further , the tubular part and the part integrally formed with one end thereof which comprise the ring reinforcement 3 are not limited to those shown in the figures , other configuration may be used as far as they are comprised of a tubular part and an other part integrally connected with the tubular part .