An intake port (19) of an internal combustion engine (11) is connected to a combustion chamber (18) and includes a connecting portion (191) having a passage cross-sectional area that increases as approaching the combustion chamber (18), and an upstream portion (192) connected to an upstream end of the connecting portion (191). The connecting portion (191) is provided at its downstream end with a valve seat (26) with which an umbrella part (32) of an intake valve (30) is brought into contact. A recess (50) extending in an extending direction of the intake port (19) and spanning the connecting portion (191) and the upstream portion (192) is provided at at least one of portions, on both sides in an extending direction of an output shaft (16), of a peripheral surface (19A) of the intake port (19).