an airflow pipe including an airflow path communicated with an internal combustion engine;

an electric air pump for generating an air stream in the airflow path of the airflow pipe;

a motion-direction conversion mechanism for converting a rotary motion of the electric air pump into a linear motion or a swing motion; and

a flow path opening/closing valve which is opened or closed by the linear motion or the swing motion of the motion-direction conversion mechanism to open/close the airflow path of the airflow pipe, wherein:

the motion-direction conversion mechanism includes:

a slider shaft movably disposed in an axial direction to perform a rotary motion integrally with the electric air pump;

a slide rotor movably disposed in an axial direction to perform a rotary motion integrally with the slide shaft;

a weight for providing a linear motion to the rotary motion of the slide rotor and also a linear motion in an axial direction to the slide shaft with a centrifugal force developed by the rotary motion of the slide rotor; and

a rolling bearing which rotatably supports the slide shaft and the slide rotor around each axis, and performs a linear motion integrally with the flow path opening/closing valve, the slide shaft and the slide rotor, wherein:

the rolling bearing includes an inner race and an outer race, one of the inner race and the outer race being fixed to the slide shaft or the slide rotor, and the other one of the inner race and the outer race being fixed to the flow path opening/closing valve.