PURPOSE: To ensure the high filling efficiency during engine operations at a high speed and under a high load and also at a low speed under a low load by providing a rotary type normally closed movable valve in a branch route connecting from an inlet passage section of a suction port to an eddy terminal section.

CONSTITUTION: A suction port 6 is composed of an eddy section B formed around a suction valve and an inlet passage section A connected tangent to the eddy section B and extending straight. A branch route 21 branched from the inlet passage section A is connected to an eddy terminal section E. A rotary type movable valve 25 is provided in the branch route 21, and it blocks the branch route 21 during engine operations at a low speed and under a low load requiring little amount of the suction air, thereby strong revolving flows are generated in a combustion chamber. During engine operations at a high speed and under a high load, the movable valve 25 is opened, and a large amount of the suction air is sent into the eddy section B through the branch route 21, thus the high filling efficiency can be ensured.