A heat exchanger includes a pair of header tanks, a plurality of flat heat exchange tubes which are disposed between the two header tanks and whose opposite end portions are connected to the corresponding header tanks, and a plurality of corrugate fins each including wave crest portions, wave trough portions, and connection portions connecting together the corresponding wave crest portions and wave trough portions, and each disposed between the adjacent heat exchange tubes. Each connection portion has a plurality of louvers which extend in a width direction of the connection portion and are arranged in a longitudinal direction of the connection portion. The louver pitch is 0.4 mm to 0.8 mm. The inclination angle of the louvers in relation to the connection portion is 20° to 30°.