A self-opened type valve is opened by motor torque of an electric motor. Therefore, a diaphragm is not necessary for opening the valve, and downsizing of a valve drive apparatus for opening the valve is possible. Since the valve is assembled to the motor shaft of the electric air pump via a motion-direction conversion mechanism, an opening action of the valve can start in a short time after a rotational action of the impeller of the electric air pump starts, so that control responsiveness is improved. At a rotation stop of the impeller of the electric air pump, the valve can be maintained in a fully closed condition by an urging force of the coil spring, thereby preventing exhaust gases or condensed water from entering into an inside of the electric air pump.