PURPOSE: To suppress the temperature rise of a center housing and to operate a supercharger smoothly for a long time by reducing the coupling area between a trubine case and the center housing or the contact area of a heat insulating board inserted between them.

CONSTITUTION: A supercharger has a turbine case 1 and a center housing 5 provided with a bearing section 7 supporting a rotary shaft 6. A heat insulating board 10 and flange section 12 are inserted to the step section 13 of the turbine case 1. The heat insulating board 10 prevents the exhaust gas from entering into an air chamber 11b. Accordingly, the heat transmitted from the turbine case 1 through the contact surface of the heat insulating board 10 and flange section 12 is decreased, and the heat transmission to the center housing 5 is reduced by half. Thereby, the temperature rise of the center housing, particularly of the bearing section 7 can be suppressed, resulting in a smooth operation for a long time.