To provide a four-cycle engine having a new supercharger which is optimum for meeting the requirements such a small size, light weight, high output, cleanliness and easiness of handling toward an internal combustion engine.

When a straight engine is divided by the respective cylinders and V-engine (using a crankshaft where opposite pistons simultaneously come to the top dead center) of a horizontal opposed type is divided taking opposed cylinders as one set, and a crank case is fitted with an intake valve 1 and a discharge valve 2 in each cylinder, in the crank case on the back of the piston, the intake and discharge process is enabled for each one rotation of the crankshaft. The air is double the exhaust amount, and introduced into the combustion chamber to always enable about doubled supercharging. The intake/discharge valve can be fitted to a pipe connecting the crank case and the intake manifold.