When a failure occurs in synchronizing mechanism, an intake air throttle valve is rotated in a direction that is opposite from a normal operational time valve closing direction, so that an arm of a driven plate contacts a throttle valve side stopper to stop rotation of the intake air throttle valve. Thereafter, when a low pressure EGR valve is rotated from a full close position to a full open position, an EGR valve side stopper contacts the arm of the driven plate to stop the low pressure EGR valve. A rotational angle of the EGR valve is sensed with a sensor and is outputted to an ECU. The ECU determines that a failure mode is set when a valve angle sensed with the sensor coincides with a rotation stop position of the EGR valve.