PURPOSE: To secure the stable joining and to obtain the heat exchanger with high performance by inserting the two heat transfer tubes of about triangle state into the approximately lozenge-shaped heat transfer tube insert hole which is set on the fin, enlarging the distance of the above heat transfer tubes and brazing in the state of no gap between the fin and the heat transfer tube.

CONSTITUTION: Air flow upstream side and downstream side heat transfer tubes 4, 5 are inserted into the approximately lozenged - shaped heat transfer tube insert hole which is set on the plane fin 2. Because the sum of width of both heat transfer tubes is smaller than the length of the longitudinal direction of the insert hole 3, so the inserting is easily executed without damaging the fin 2. Next by enlarging the distance of both heat transfer tubes 4, 5, the heat transfer tubes 4, 5 are brought respectively into contact with two side of the up and down stream direction sides of gas flow of the insert hole 3. The brazing material clad to one or both surfaces of the fin 2 is brought to flow in their contact surface and joint the both with the brazing in the furnace. Therefore, the brazing is completely and stably executed.