PURPOSE: To prevent deterioration of the performance of the supercharger by a method wherein gas such as EGR gas, blow-by gas or the like, which is added to suction gas, is permitted to be introduced into the suction system of the engine without exerting the supercharger with adverse effect, in the engine equipped with the supercharger.

CONSTITUTION: The engine 1, equipped with the supercharger, is provided with a main suction gas path 14 and a supercharging path 18 in which the supercharger 19 is arranged. At least under high load of the engine, supercharged air is supplied from the supercharging path 18 in the compression stroke of the engine in addition to natural suction from the main suction gas path 14. The engine is further provided with an introducing path 30 for EGR gas, which is extended from an exhaust path 31, and the introducing path 32 for blow-by gas, which is extended from a crank chamber 33. Both introducing paths 30, 32 are opened in the main suction path 14 at the downstream side of a main throttle valve 17. Accordingly, the EGR gas and the blow-by gas, which are added to the suction gas, are supplied into a combustion chamber 6 through the main suction gas path 14, therefore, the supercharger 19 will never be affected adversely by the gas added to the suction gas.