A diaphragm is provided in a pump case so as to define a pump chamber communicated with an external member having an air chamber. A motor actuates the diaphragm to introduce air into the pump chamber and to supply the introduced air to the air chamber. An exhaust valve exhausts air in the pump chamber to lower a pressure in the air chamber. The exhaust valve is provided with a valve body and an actuator which is driven by the motor to actuate the valve body so as to open or close an exhaust port communicated with the pump chamber.