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.