There is disclosed a four-cycle engine in which a crankshaft and a cam shaft are disposed generally parallel to each other, and an intake port and an exhaust port are formed in a cylinder head. The intake port and the exhaust port are arranged in such a manner that a line passing through the centers of the intake port and the exhaust port is non-parallel to the axis of the crankshaft. With this arrangement, an intake passage and an exhaust passage can be greatly shortened, and therefore intake efficiency as well as exhaust efficiency can be enhanced, thereby enhancing the performance of the engine. In an air-cooled engine, the overheating of the engine is greatly restrained.