Abstract: A common intake port 10 is branched into a pair of branch intake ports 12, 24, which are separated through a partition wall 11, at the downstream end thereof. A pair of intake valves 16, 17 adapted to independently open and close the pair of branch intake ports 12, 14, respectively, are provided. In a four-stroke cycle internal combustion engine 1 adapted so that one 16 of the pair of intake valves 16, 17 opens and closes in a low intake air operating range, while the other intake valve 17 is in a resting condition, and that both the pair of intake valves 16, 17 open and close in a high intake air operating range, a cutout 57 is formed in a laterally central portion of the partition wall 11 in such a way as to extend from the edge of the upstream end of the partition wall 11 toward the downstream end thereof and to separate the pair of branch intake ports 12, 14 from each other.