PURPOSE: To obtain the reliable cooling action by effectively making use of the thermosyphon effect without using any circulating pump to be operated after the stop of an internal combustion engine, by providing respective check valves to a feed pipe and a return pipe of a centrifugal supercharger and specifying respective pipe structures.

CONSTITUTION: A centrifugal supercharger 2 having a water-cooled bearing housing 3 is attached to an internal combustion engine 1. The bearing housing 3 is connected to a feed pipe 4 and a return pipe 6 and a cooling mechanism of the internal combustion engine 1. In this case, a check valve 5 for limiting the flow only in the direction from the internal combustion engine 1 to the centrifugal supercharger 2 is provided on the feed pipe 4. While, the return pipe 6 is branched into a first pipe 10 connected to an adjusting vessel 8 above the cooling fluid level 12, and a second pipe 11 to be connected to the adjusting vessel 8 below the cooling fluid level 12. Moreover, a check valve 7 is provided on the second pipe 11 so as to allow the flow from the centrifugal supercharger 2 to the adjusting vessel 8.