In an electromagnetic clutch, a rotor includes a cover portion that covers a radially outer end of an armature from a radially outer side. The cover portion, the radially outer end of the armature, and a wall of the rotor define a discharge passage that is formed into a ring shape centered on a rotating shaft and is open on a first end side in an axis line direction for discharging abrasion powder generated by friction between walls. The cover portion includes a tapered surface that is shaped such that an area in a cross sectional plane of the discharge passage which is orthogonal to an axis of the rotating shaft becomes larger toward the first end side in the axis line direction.