Patent ID: 8736125

Claim:
A coupling device comprising: a cylindrical magnet rotator including magnets so arranged that different magnetic poles alternately line up in a circumferential direction; and a cylindrical yoke-side member, including a conductor portion made of a nonmagnetic material and a yoke, arranged on the inner side or the outer side of said magnet rotator to be relatively rotatable in a state not in contact with said magnet rotator, wherein said conductor portion of said yoke-side member has a plurality of first conductor portions arranged to extend in a direction of the axis of rotation at a prescribed interval in said circumferential direction at least on a side opposed to said magnets, said yoke of said yoke-side member is at least arranged on said side opposed to said magnets in a clearance between said plurality of said first conductor portions, and the ratio between the circumferential length of each of said first conductor portions and the circumferential length of said yoke arranged in said clearance between said first conductor portions (circumferential length of each first conductor portion/circumferential length of yoke) is at least 1/1.4.