PURPOSE: To prevent the cooling water of a turbocharger from drying up by connecting the cooling water passage of water-cooled turbocharger to the cooling water system of a water-cooled intercooler and provided at least a part of said cooling water system on the upper part of said cooling water passage of said turbocharger.

CONSTITUTION: The water jacket of an engine 1 is connected in alignment to a radiator 3 via a cooling water passage 4 and a thermostat 14, and the radiator 3 is connected to the suction side of a water pump 2 via a return passage 5. A passage 6 is branched off of the cooling water passage 4 on the upper course side of the thermostat 14 and connected to the water jacket of a turbocharger 7. Also, a passage 13 is branched off of the middle part of the passage 6 and a sub-radiator 9 for intercooler, a motor-driven water pump 10, and an intercooler 11 are connected in series to this passage 13. And, the intercooler 11 is provided on the upper part of the turbocharger 7 to prevent the cooling water in the cooling water passage of the turbocharger from drying up.