A solenoid actuator is mountable to a mounting surface of an engine, such that an accommodated portion is inserted into the engine, and an exposed portion is located outside the engine. An operating portion operates when a solenoid actuator portion is energized and de-energized. A main body forms at least a part of an outer shell of the exposed portion. A connector portion is projected from the main body in the exposed portion. The connector portion is connected with a wiring for the solenoid actuator portion. At least one protrusion is projected radially outward from a sidewall of the main body in the exposed portion. The at least one protrusion is located at a position different from the connector portion in a circumferential direction of the sidewall. The at least one protrusion forms a clearance with the mounting surface in an axial direction.