An engine unit includes an engine and a power train which are disposed in parallel to each other. The power train includes a transmission and a differential. The engine and the power train are housed in one engine housing formed of upper and lower parts which are mated with each other along respective mated surfaces. Upper halves of bearings for the crankshaft and upper halves of bearings for a rotational shaft of the power train are formed in the mating surface of the upper part of the engine housing and lower halves of bearings for the crankshaft and lower halves of bearings for said rotational shaft of the power train are formed in the mating surface of the lower part of the engine housing. The upper part of the engine housing is formed integrally with the cylinder block of the engine.