To improve moldability and heat exchanging performance in a tube for a heat exchanger having high pressure resistant request by arranging a heat transfer enlarging part having a medium channel not formed at both or one side end of a tube section, and perforating a hole in which a medium does not flow, in the enlarging part.

The tube 2 for a heat exchanger comprises a plurality of refrigerant channels 9 formed at its center to communicate in a longitudinal direction, and a heat transfer enlarging part 2a arranged at both or one side end to enlarge a heat transfer area. Then, to assure high pressure resistance, its sectional shape is formed in a circular shape. Meanwhile, A hole 10 of a rectangular section coincident with a sector flat surface shape of the tube 2 is perforated at the part 2a. In the case of extrusion molding the tube 2 of a metal material or the like, a core material for forming the hole 10 is disposed at a part for arranging the part 2a to improve moldability. The tube 2 can be reduced in weight and cost by such a hole 10, and its heat transfer area is increased.