CLUTCH

PROBLEM TO BE SOLVED: To increase clutch transmission torque in a self-hold type clutch.SOLUTION: A projection 531d extending in a rotational axis direction is provided in a spool 531 of a first electromagnetic coil 53, and a yoke 55 is fitted to the outer peripheral side of the projection 531d. The yoke 55 is held by the spool 531 with higher dimensional accuracy and form accuracy than a permanent magnet 51, and thereby vibration of the outer peripheral surface of the yoke 55 with respect to the rotational axis can be suppressed. Consequently, a gap S provided on the outer peripheral side of a movable body 52 is made small, and clutch transmission torque can be increased.