A diaphragm is provided in a pump case so as to define a pump chamber communicated with an external member having an air chamber. The actuator is provided in the pump chamber. An exhaust valve is provided with a valve body, formed with a slit through which air the pump chamber is exhausted, and a screw member, screwed into a first wall of the pump case to adjust an opening amount of the slit by a screwed amount thereof, thereby adjusting an exhausting rate of the air in the pump chamber. The pump case is formed with a ventilation hole communicated with the pump chamber to allow the air exhausted from the slit to pass through.