PURPOSE: To prevent the occurrence of a torque shock by a method wherein when the number of revolutions of an engine exceeds a given value, a speed at which an exhaust gas return valve is closed is controlled to a low value, and when the number of revolutions of an engine is below the given value, a speed at which the exhaust gas return valve is closed is controlled to a high value.

CONSTITUTION: A control unit 30, based on an engine load detecting signal, throttles the passage area of a negative pressure passage 24 to a given value in a high number of revolutions of engine running region, in which the high number of revolutions of an engine exceeds a given value, by means of a negative pressure throttle valve 27. The control unit fully closes the passage area of the negative pressure passage 24 when the number of revolutions of an engine is below a given value. Thus, in the high number of revolutions of engine running region, a change in a pressure in a negative pressure chamber 21 is only gradually produced, the opening and closing speed of an exhaust gas return passage 8 by means of an exhaust gas return valve 9 is reduced, and exhaust gas return is gradually suspended or restarted. This constitution prevents the occurrence of a torque shock through suspension or restart of exhaust gas return, and keeps a running feeling at an excellent state.