The invention provides an electromagnetic actuator (30) comprising an electromagnetic drive unit (31) for forming a magnetic path (C) between a plunger (37) made of a magnetic material and an inner yoke (36), thereby to drive the plunger (37) in an axial direction by an electromagnetic force. Further comprised is an operation unit (32) having a dog (41) made movable along the axial direction between a coupled position, at which the dog is coupled to a partner part, and a released position, at which the dog is released from the partner part, thereby to constrain the partner part in the circumferential direction when the dog (41) is at the coupled position. Still further comprised is a stop ring (45) interposed between the plunger (37) and the dog (41), for allowing the circumferential relative movement of the dog (41) to the plunger (37) but restraining the relative movement in the axial direction.