PURPOSE: To eliminate after-burn and to reduce oil consumption of an internal combustion engine, by providing, at an intermediate portion of a by-pass air passage 7, a means 8 for introducing air at the time of deceleration of the engine which includes two diaphragm means 13, 14 arranged in a tandem form.

CONSTITUTION: At an intermediate portion of a by-pass air passage 7, there is provided an apparatus 8 for introducing air at the time of deceleration of an engine, which consists of a valve chamber 9 having an inlet passage 9A and an outlet passage 9B connected respectively to a passage 7A on the side of an air cleaner and a passage 7B on the side of an intake passage of the by-pass air passage 7 that is divided into the two passages 7A and 7B, a valve element 11 disposed in said valve chamber 9 for establishing or interrupting communication between the inlet passage 9A and the outlet passage 9B selectively, and the device 8 for introducing air at the time of deceleration consisting of the two diaphragm means 13, 14 disposed at an upper portion in the valve chamber 9 in a unitary manner for driving the valve element 11 by a rod 12.