INTERNAL COMBUSTION ENGINE

A water jacket (21) is divided by a partition wall (23) which has a flat plate shape, into a first water jacket portion (24) on a cylinder head side, and a second water jacket portion (25) on a cylinder block side. The partition wall (23) is connected to a connection portion between a top wall (12) of a combustion chamber (5) and an exhaust port wall (7), on one side surface side of an internal combustion engine (1), with respect to the combustion chamber (5). The partition wall (23) is connected to a portion of an upper end side of a cylinder wall (16) which constitutes a side wall of the combustion chamber (5), on the other side surface side of the internal combustion engine (1), with respect to the combustion chamber (5). A knock sensor mounting boss (26) is provided on the other side surface side of the cylinder head (3), on an extension line of the partition wall (23).