PURPOSE: To operate an opening of the valve both for rapid and gradual deceleration, and make an air-fuel ratio constant at all deceleration time, by constructing the valve and valve stem into a separate unit, and interposing a different spring between the both, in the device where a feed of air is performed at the time of deceleration of the engine.

CONSTITUTION: The upstream of a Venturi 2 and the downsream of a throttle valve 3 are linked by an air path 7 having an inlet port 5 and an outlet port 8. In this path 7, is arranged a normally-closed deceleration valve 10 by a strong tension of a spring 11. And to this valve 10, is contacted a valve stem 15 pressed by a weak tension of a spring 13, simultaneously to the other end of this valve stem 15, is contacted a diaphragm 21 of a servo mechanism 20. And the valve 10 is opened and closed by an intake suction conducted into a negative pressure chamber 16. At the time of rapid deceleration of the engine, its high suction is directly applied to the surface of the valve 10 from the path 7, to open the valve 10, and at the time of gradual deceleration, a suction, applied to the negative pressure chamber 16, slightly opens the valve 10 through the valve stem 15.