The invention aims to prevent the dust passing through a gap provided for sliding movement of bypass valve from being attached to a screw mechanism, and thus to guarantee smooth motion of the screw mechanism. Provided is a bypass-intake-flow control apparatus including a throttle body in which a bypass and a valve hole that is open into the course of the bypass are formed. A bypass valve to open and close the bypass is slidably but not rotatably fitted into the valve hole. An actuator is attached to the throttle body with an output shaft arranged coaxially with the bypass valve. The screw mechanism links the output shaft and the bypass valve. A bottomed hollow portion is formed in the bypass valve with an opening facing the actuator. A dust cover that surrounds the screw mechanism in the hollow portion is attached to the throttle body.