An intake port of an internal combustion engine is connected to a combustion chamber and includes a connecting portion having a passage cross-sectional area that increases as the connecting portion approaches the combustion chamber, and an upstream portion connected to an upstream end of the connecting portion. The connecting portion is provided at its downstream end with a valve seat with which an umbrella part of an intake valve is brought into contact. At least one recess extending in an extending direction of the intake port and included in the connecting portion and the upstream portion is provided at least at one of two portions, the two portions located on both sides in an extending direction of an output shaft, of a peripheral surface of the intake port.