To secure each core part of a corrugate fin type heat exchanger while keeping in an ideal shape by arranging a pair of independent intermediate retaining member at the hollow part of each core, securing each intermediate retaining member to the side end of first and second cores through a bar member and then securing each part by brazing.

A heat exchanger being employed suitably in motorcycle comprises a large number of flat tubes 1 and gate fins 2 juxtaposed alternately, and a core 4 formed by passing the opposite ends of each flat tube 1 through a tube plate 3. The core 4 has a hollow section 5 at the intermediate part in the arranging direction of the flat tube 1 and core parts 4a, 4b are provided on the opposite sides. A pair of independent intermediate retaining members 7 are disposed at the hollow section 5 in parallel with the tube 1. Side end of each core part 4a, 4b and the intermediate retaining member 7 are fastened by means of a bar 8 and then each parts of the core 4 are brazed in the furnace. Subsequently, the intermediate retaining member 7 and the bar 8 are removed to produce the core 4.