PURPOSE: To greatly reduce pumping loss by providing a limited open rate setting means for setting according to detected engine speed the maximum limited open rate at which pressure inside a combustion chamber is roughly at its maximum when an inlet valve is closed, and an open rate limiting means for regulating the maximum open rate of a first switching valve according to the set maximum limited open rate.

CONSTITUTION: A second switching valve F is interposed in a communicating passage E which communicates with an inlet passage C located on the lower side of a first switching valve D. Next, engine speed is detected by a throttle valve H and the maximum limited open rate at which combustion pressure is roughly at its maximum when an inlet valve A is closed is set by a means I according to the detected engine speed. The maximum open rate of the first switching valve D is regulated by the means I according to the set maximum limited open rate. Thereby changes in intake pressure inside a combustion chamber during an intake stroke are subjected to optimal control so as to enhance the effects of reducing pumping loss.