PURPOSE: To cool compressed air properly at all times by providing means which detects at least the temp. of an engine, controlling an water pump in line with the engine temp. and, thereby, controlling the cooling capacity of an inter-cooler.

CONSTITUTION: Air sucked through an air filter 1 is compressed by a turbo- supercharger 2 and, after cooled by an inter-cooler 3, sent into an engine 4. Cooling water in a water tank 7 is sent into the inter-cooler 3 by means of a water pump 5, and the cooling water with a raised temp. by absorbing the heat of said air is cooled by means of a radiator 6. When the temp. of the engine 4 detected by a temp. sensor 12 rose above a set value, the temp. of compressed air detected by a sensor 10 and the temp. of cooled air detected by a sensor 11 are fed into a temp. detecting circuit 13. And, the water pump 5 is controlled by means of a pump controlling circuit 14, to adjust the quantity of cooling water to be sent into the inter-cooler 3.