PURPOSE: To improve comfortableness, by measuring the speed of wind at an external air inlet port to control the degree of opening of an internal and external air changeover door in such a direction as to reduce the quantity of introduced external air as the speed of wind increases, so that the temperature of the riding room of a vehicle is prevented from changing.

CONSTITUTION: A controller 15 receives a set temperature 16, the temperature 17 of internal air, the temperature 18 of external air, the quantity 19 of insolation and the speed 20 of wind at an external air inlet port to regulate a blower 5, an internal and external air changeover door 3 and an air mix door 8. When the wind speed 20 is not higher than 8m/s, the changeover door 3 is kept in a position C, the quantity of introduced external air is maintained at 30% and no compensation is effected. When the wind speed 20 is 10W18m/s, the changeover door 3 is put in a position B and the quantity of introduced external air is set at about 25%. When the wind speed 20 is not lower than 20m/s, the changeover door 3 is put in a position A and the quantity of introduced external air is set at about 20%. The temperature of the riding room of a vehicle is thus prevented from changing depending on the wind speed 20, so that comfortableness is improved.