PURPOSE: To obtain a structure for preventing deflection by a simple manufacturing process, in a heat exchanger having a long effective length.

CONSTITUTION: A seat 9 between fins is arranged between the neighboring fins 7, 7 of a heat exchanger, arranged so as to be slanted and having a long effective length, from the lower side of the same while the seat 9 between fins is retained to a refrigerant tube 8. A reinforcing plate 10 is arranged so as to be abutted against the lower end of the seat 9 between fins and both lengthwise ends of the reinforcing plate 10 are fixed respectively to the front plate and rear plate of the heat exchanger to prevent the deflection of the heat exchanger by the seat 9 and the reinforcing plate 10. According to this method, a means to prevent the deflection after incorporating original functional parts into the heat exchanger can be incorporated whereby workability can be improved.