PURPOSE: To prevent the rise of supercharging pressure above a fixed pressure by controlling a bypass valve through the utilization of the force which acts onto the bypass valve due to exhaust pressure.

CONSTITUTION: On the casing 6 of an exhaust turbine 3, an exhaust bypass passage 7 is drilled which bypasses the exhaust turbine 3. The bypass passage 7 forms valve seat 8 midway and is equipped with a bypass valve 9. Accordingly, to the valve seat side of the bypass valve 9, the exhaust pressure on the exhaust turbine 3 inlet side is applied, and to the opposite side, the spring force of a pressing spring 14 is applied, and so the bypass valve 9 is controlled, and the supercharging pressure is controlled to a fixed value.