INTERNAL COMBUSTION ENGINE AND STRADDLED VEHICLE

An internal combustion engine (20) includes a crankcase (30), a cylinder body (40), a cylinder head (50), a cylinder head cover (60), a cam chamber (70), a cam chain chamber (80), a crankshaft (22) disposed in the crankcase, a cam shaft (71) disposed in the cam chamber and the cam chain chamber, a cam chain (81) disposed in the cam chain chamber, a cam chain guide (83A) to guide the cam chain, a chain tensioner (82) to press against the cam chain via the cam chain guide, and a rib (90) disposed in the cam chain chamber in such a manner as to restrain a lift of the cam chain. The rib is monolithically formed with the cylinder head. The rib includes a portion located upstream of a meshing start position (SP) at which engagement between the cam chain and the driven sprocket wheel begins.