To provide a heat exchanger enhancing pressure tightness, and generating hardly plugging in a tube hole.

This heat exchanger is provided with flat tubes 11 and a tank part 20, the tank part 20 is provided with structure integrated, by brazing, with a plate header 50, a tank header 30, and an intermediate plate 40 interposed between the plate header 50 and the tank header 30, the intermediate plate 40 is formed with a flat plate hole 41 inserted with a tip part of the flat tube 11, the tank header 30 has a plane part 31 joined to the intermediate plate 40, and a bulged part 32 bulged to an opposite side of the intermediate plate 40, and for forming a coolant flow channel 33 communicated with each flat tube 11 via the plate hole 41, and the plate hole 41 has narrow width parts 42a, 42b with short direction widths Wa, Wb formed partially narrowly, in the vicinity of boundary parts 34a, 34b between the bulged part 32 and the plane part 31.