PURPOSE: To improve the reliability and the safety by arranging a heat exchanger having a heater and a cooler partitioned through a partition board in the intake path at the downstream of supercharger while a switching valve at the intake air inlet of heater and holding in standstill condition under non- drive condition.

CONSTITUTION: The heat exchanger 1 is provided with many vertical cooling tubes between the upper and lower headers (only the upper header 6 is shown) and defined into a cooler 10 and a heater 11 through a partition board 9. A switching valve 25 is provided to the air-duct 20 between the intake gas inlets 18, 19 of the cooler 10 and the heater 11 to be switched between the heater close position P and the cooler close position Q through operation of the cylin der 33. While one end of lever 36 of holder 35 is secured to the shaft 26 of the switching valve 25 and the other end of said lever 36 is coupled to the operating rod 40 of compression spring mechanism 39 to hold the switching valve 25 at the switching position under non-driving of cylinder 33.