To excellently braze all of respective connecting parts regardless of the difference in the surface area to the weight of respective composing members.

A relatively low liquidus temperature of brazing filler metal is used as a first brazing filler metal layered on the surface of respective headers 2a, 2b having the narrow surface area to the weight. To the contrary, a relatively high liquidus temperature of brazing filler metal is used as a second brazing filler metal layered on the surface of respective flat heat transmitting tubes 3 and inner fins having the wide surface area to the weight. The first and the second brazing filler metals are about simultaneously molten regardless of the difference in temperature at the time of heating, whereby all of respective connecting parts are excellently brazed.