A breather structure of an actuator includes: a breathing hole that extends through a rear housing between an inside and an outside of the rear housing; a filter that is configured to permit a flow of gas through the breathing hole via the filter while limiting a flow of liquid and a flow of solid through the breathing hole between the inside and the outside of the housing; and a blocker. The blocker is configured to block a portion of a path extending from an outer opening, which is an opening of the breathing hole opened to an outside space, to the filter to limit arrival of the liquid and the solid from the outside space to the filter.