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 to the air chamber . an exhaust valve exhausts air in the pump chamber to lower a pressure in the air chamber . in the exhaust valve , an exhaust port is communicated with the pump chamber . a flexible valve body having a larger size than the exhaust port is disposed so as to close the exhaust port from a side facing the pump chamber . an actuator is disposed in an opposite side to the valve body relative to the exhaust port , and driven by the motor so as to be movable between a first position retracted from the exhaust port and a second position passing through the exhaust port so that the valve body is actuated so as to open the exhaust port . an urging member always urges the actuator to the first position thereof .