PURPOSE: To prevent small vibration in the direction of axial line of a rotor and to rotate the rotor in a still state by displacing the average position of distribution in the direction of axial line of magnetic force discharged from a plurality of magnetic poles of the rotor toward a counter-catching part side.

CONSTITUTION: In an annular magnet 17 which are alternately provided with a number of N and S magnetic poles around a rotor 15, a thickness T2 of an edge part 17a at the opposite side of a contacting part 19 contacting a catching part 10 of a case 1 is formed to be larger than a thickness T1 of the other part 17b. Then, a magnetic force distribution average position in the direction of the axial line of the rotor 15 is displaced to the opposite side from the catching part 10 as compared with the magnetic force distribution average position of magnetic force discharged from a number of magnetic pole pieces 7 and 8. Therefore, since the rotor 15 is retained while the contacting part 19 is constantly pressed to the catching part 10 when feeding AC current to a coil winding 13 of a coil 11 and rotating the rotor 15, the small vibration in the direction of axial line of the rotor 15 and rotating the title motor quietly.