PURPOSE: To obtain a compact engine by arranging a suction pipe and a throttle chamber on the upper side of the right and left banks of the engine and arranging an intercooler an auxiliaries on a crankcase.

CONSTITUTION: In a horizontally opposed type engine equipped with the right and left cylinder heads 2, auxiliaries such as alternator 4 are arranged on the upper front side of a crankcase 3, and driven by a crankshaft through a belt transmission system 6. Behind the auxiliaries, a box-shaped water-cooled intercooler 8 is arranged and allowed to communicate with each suction pipe 9 installed in the right and left banks through a throttle chamber 10 arranged in correspondence with each bank. An air feeding pipe 11 communicates with the water-cooled intercooler 8 through a supercharger 12 arranged behind the right and left banks. By such constitution, the compact constitution of the engine can be realized without increasing the space used exclusively and height as a whole, even if the water-cooled intercooler 8 is installed as the equipment for the supercharger 10.