To provide a method for inspecting air-tightness of a heat exchanger in which the method for inspecting air-tightness can be simplified while reducing the cost required for inspection.

In one method for inspecting air-tightness of a heat exchanger 5 being used in a cooler 1, an outdoor air fan 6 is operated under a state where an outdoor air outlet 4b is closed air-tightly by applying a cover 13 thereto. Inner pressure of the cover 13 is introduced to a pressure gauge 15 through a pressure introduction pipe 14 connected with the cover 13. A decision is then made whether air-tightness is acceptable or not based on a pressure rise value measured by the pressure gauge 15. Since the outdoor air fan 6 provided in the cooler 1 is used as a pressurization source in the method for inspecting air-tightness, an additional pressurization source, e.g. a pressure pump, is not required. Consequently, air-tightness can be inspected conveniently as compared with a case using a pressurization source, e.g. a pressurization pump, and the cost required for inspection can be reduced.