To reduce an operation force when cutting off power transmission by moving a magnetic coupling control body along the rotating axes of first and second rotors.

A pulley side rotor 10 and a shaft side rotor 20 keep in parallel a plurality of projected parts 12, 22 along a peripheral direction taking each rotating axis as a center on individual end surfaces so as to be opposite to each other, and a magnetic coupling control body 30 containing a permanent magnet 31 are arranged in the pulley side rotor 10 and shaft side rotor 20 so as to be movable along the rotating axes. States magnetically coupled and magnetically uncoupled by a permanent magnet 31 between the projected parts 12, 22 opposed to each other are switched through the movement of the magnetic coupling control body 30.