PURPOSE: To make it possible to make compact the size of an air conditioner as well as its installation space and enhance the efficiency of heat exchanger by providing curved-heat radiation fins.

CONSTITUTION: There is provided a heat exchanger having a large number of heat radiation fins 12 installed side by side with a small clearance to each other where heat exchanger tubes are penetrated into these heat radiation fins 12. The heat radiation fins 12 are formed in the shape of a curved surface while the fin width dimension LB in the central part B is formed more widely compared with the width dimensions La and Lb of the upper and lower parts of the fins on the both ends A and C.