An internal combustion engine including: a cylinder block in which a plurality of cylinders are formed; and a cylinder head formed in conjunction with the cylinder block into one body to form a plurality of combustion chambers, wherein an upper surface of the cylinder head is divided, along a direction in which the plurality of cylinders are arranged, into first regions that are regions that overlap the combustion chambers as viewed from an axial direction of the cylinders and a second region that is a region located between two of the first regions adjacent to each other, and at least either an intake-side cam journal or an exhaust-side cam journal is disposed in the second region.