PURPOSE: To eliminate damage even if a force is applied in an accidental manner by disposing magnet pieces directed in the magnetic force direction of a circumferential direction at equal intervals on the whole periphery in the circumferential direction, and reversely directing the magnetic force directions of the disposed pieces at the adjacent pieces.

CONSTITUTION: Magnetic pieces 3, 4 of a predetermined length (a) of circumferential direction are disposed at a predetermined circumferential interval (b) at the peripheries of wheels 1, 2. The magnetic force directions of the pieces 3, 4 are all directed in the circumferential direction, but reversely in the magnetic force directions. The wheels 1, 2 are brought into contact or close to each other at the peripheries. When either wheel is rotated, the other wheel is rotated by the attracting effect of the pieces 3, 4. Thus, a power transmission wheel having no damage and wear of gears, no noise due to engagement of the gears or no necessity of lubricant is obtained.