PURPOSE: To permit supercharging by utilizing a part of wind pressure in the front surface of the vehicle by a method wherein the suction air introducing device of an internal-combustion engine for vehicle is provided with a supercharging opening faced to the advancing direction of the vehicle and a waterdrop separator accommodating an automatic water discharging valve.

CONSTITUTION: The suction air introducing path in an internal-combustion engine for vehicle is provided with an air intake 1 opening toward the advancing direction of the vehicle and air, supercharged by the running wind of the vehicle, is introduced from the air intake 1 into the tangential direction of the waterdrop separator 3 through a connecting tube 2. Drops of rain in the air are discharged out of the automatic water discharging valve 4 provided at the lower end of the waterdrop separator 3 and the air only is introduced into the suction pipe 6 of the internal combustion engine through a connecting pipe 5.