A collecting exhaust port 18 provided in a cylinder head 12 is comprised of exhaust port sections 46 extending from exhaust valve bores 35 in cylinders 14, and an exhaust collecting section 47 in which the exhaust port sections 46 are collected. The cylinder head 12 includes a protrusion 49 projecting in an arch shape outside a side wall 111 of a cylinder block 11. The exhaust collecting section 47 of the collecting exhaust port 18 directly faces an inner surface of a side wall 12 of the protrusion 49. Water jackets J2 and J3 for cooling the protrusion 49 are provided in upper and lower surfaces of the protrusion 49 having the collecting exhaust port 18 defined therein. The water jackets J2 and J3 are not provided between the side wall 121 of the protrusion 49 and the exhaust collecting section 47. Thus, the compact cylinder head 12 having the collecting exhaust port 18 integrally provided therein can be formed, while avoiding the complication of the structure of a core.