Simplifying a water circulation structure of a cylinder block and realizing a compact layout of piping connecting an engine body and a radiator.
A water-cooled internal combustion engine (E) is provided with an engine body including a cylinder block (20) and a cylinder head (21), and a radiator (52). The radiator (52) is disposed separated, in a prescribed direction, i.e. in a rightward direction, from the engine body. A chain chamber (44) which accommodates a transmission mechanism, including a chain, for a valve system is provided in end portions (20e and 21e), which are located rightwardly toward the radiator (52), of the cylinder block (20) and the cylinder head (21), respectively. A cooling water outlet portion (61) open to a cylinder head water jacket (Jh) is provided in the end portion (21e) of the cylinder head (21), the cooling water outlet portion (61) being connected with an inlet pipe (57) for leading the cooling water having flowed out of a cylinder block water jacket into the cylinder head water jacket Jh to the radiator (52). The cooling water outlet portion (61) is disposed rightwardly closer to the radiator (52) than the chain chamber (44).