PURPOSE: To improve the charging efficiency during a high speed and high load operation by fitting a closing valve in a branch path connecting between the inlet passage and volute end section of a helical suction port of a supercharged internal combustion engine and by opening or closing said valve in accordance with the supercharged pressure.

CONSTITUTION: In an internal combustion engine provided with a supercharger composed of a suction compressor C and an exhaust turbine T, the inlet passage section A of a helical suction port 6 and the volute section B end section formed around a suction valve connected to the inlet passage section A are connected to each other by a branch section 14, which is opened or closed by a rotary valve 18. An actuator 63 is connected to the valve axis 20 of the rotary valve 18 through an arm 22 and a rod 62, and the rotary valve 18 is controlled in accordance with the pressure in a suction passage 34 downstream the compressor C. That is, when the pressure in the suction passage 34 exceeds a preset value, said pressure actuates the actuator 63 to open the valve 18.