PURPOSE: To reduce a pumping loss so sharply in a simple structure as well as to improve the extent of output torque at time of low load by installing a first on-off valve, being controlled synchronously with engine speed, and a second on-off valve, being controlled on the basis of the engine speed, both in an interconnecting passage to be interconnected to the downstream of a throttle valve installed at each cylinder, respectively.

CONSTITUTION: When a piston goes down, an intake valve A is opened, inhaling air into a combustion chamber B. In this case, an intake passage C being interconnected to the intake valve A of each cylinder is opened or closed by a throttle valve D. In addition, an interconnecting passage E at least being interconnected to the intake passage C at the downstream of the throttle valve D is installed there, and a first on-off valve F and a second on-off valve G in series with the former both are installed in this interconnected passage E. The first on-off valve F is synchronized with engine speed and controlled by a first driving control means H. On the other hand, the second on-off valve G is controlled by a second driving control means I on the basis of engine speed. With this constitution, an intake pressure variation at the combustion chamber in an intake stroke is optimally controlled, through which the reduced effect of a pumping loss is sharply improved.