To ensure an integrated soldering in a double heat exchanger by suppressing deformation of a tube in the integrated soldering work.

Supports 114 extending in the short diameter direction is installed in the inside of the first tube 111 of a flat radiator 110 in a double heat exchanger 100 in which condensers 120 are arranged parallel below the radiator 110. Thus the first tube 111 is hardly deformed in the direction of the short diameter of the flat tube, even when a compression force is applied in the direction of the short diameter in order to securely solder the adjacent first tube 111 and the first fin 112, and the adjacent second tube 121 and the second fin 122 to each other. Thus, soldering can be performed easily, and the increase of water flow resistance due to the deformation can be avoided.