To achieve compactness of outer size of a heat exchanger, and achieve universality of parts.

The flat tubes 5 and 6 are formed flat to have a fluid passage inside, with both ends opened, and they are twisted close to opening end parts 13 and 14, as they are inserted into tube inserting holes 7, 8, and 12, that are extended along the center lines of header pipes 2, 3, and 4. The opening end parts 13 and 14 are provided to be offset to the center lines in the lengthwise direction, in such offset quantity that the opening end parts 13 and 14 coincide with side edges. Outer size of the heat exchanger can thus be compact. Parts can be commonly used.