To provide a method for forming an integrated internal baffle with high bursting strength without any leak in an end part and a fin type heat exchanger.

In this method, a manifold is immovably (permanently) pressed and collapsed in a prescribed position so that a manifold wall top part 50 and a manifold wall bottom part 52 form about a U shape recessed part 58, and a slit is formed in the U shape recessed part. A brazing filler metal is applied to the manifold, and the manifold is treated so that the brazing filler metal is made to flow through the slit and between the manifold wall top part 50 and the manifold wall bottom part 52 at the time of brazing and whereby the manifold wall top part 50 and the manifold wall bottom part 52 are mutually fixed.