PURPOSE: To make the effective use of the capacity of a heat exchanger by a method wherein the heat exchanger is divided into two parts one of which has its fins arranged at narrow intervals while the other has its fins arranged at wide intervals and the former part of the heat exchanger is arranged closer to a blower than the latter part so that the quantity of air passing through the heat exchanger is equalized.

CONSTITUTION: The heat exchanger 9 is divided into an upper heat exchanger 9a and a lower heat exchanger 9b and the fins of the upper heat exchanger 9a are arranged at intervals of (α-a) while those of the lower heat exchanger 9b are arranged at intervals of (α+a). Accordingly, the resistance in the air flow passage in the heat exchanger 9a having narrow inter-fin intervals becomes larger than that in the air flow passage in the heat exchanger 9b so that the quantity of air passing through the heat exchanger 9 is more equalized than in the case of the conventional heat exchanger and the heat exchange capacity of the heat exchanger can be made use of effectively. Further, since the velocity of air passing through the heat exchanger is equalized, the whistling sound of air running against the heat exchanger is lowered to thereby reduce noises.