NOVELTY - Coating liquid (12) flows in circulation path from tank member (5a) of downward direction position after a heat exchanger (1) is arranged when up-and-down reverse rotation of heat exchanger is performed. Coating liquid is then ejected from the circulation path after liquid level of coating liquid flows in downward direction position from tank member (5a) of upper position, and flows to position which exceeds last liquid level.    USE - For forming coating layer to heat exchanger used by cooling system of fuel cell electric vehicle.    ADVANTAGE - Prevents coating layer formed at the bottom face of tank member of upper position from becoming thick. Also prevents coating layer formed at the bottom face of tank member of downward direction position from becoming thick. Faults, such as peeling of coating film resulting from film thickness of coating layer, and deterioration of heat exchange capability are prevented. Ensures easy application of coating liquid.    DETAILED DESCRIPTION - Coating liquid flows in circulation path from tank member of downward direction position after a heat exchanger is arranged when up-and-down reverse rotation of heat exchanger is performed. Coating liquid is then ejected from the circulation path after liquid level of coating liquid flows in downward direction position from tank member of upper position, and flows to position which exceeds last liquid level. The longitudinal direction (L) of a tube (2) is arranged in up-down direction of the heat exchanger (1). Coating liquid (12) flows in circulation path from the tank member (5a) of downward direction position. Coating liquid is ejected from the circulation path after liquid level of coating liquid flows to downward position direction rather than to the tank member (5b) of upper position.    DESCRIPTION OF DRAWING(S) - The figure shows injection state of coating liquid in first application process.    Heat exchanger (1)    Tube (2)    Tank member (5a)    Coating liquid (12)    Longitudinal direction (L)