To provide a flat tube for a heat exchanger and a heat exchanger for a vehicle or the like, capable of overcoming the disadvantage of a flat tube used in the conventional heat exchanger, wherein the area of a joint part forming a passage is small, the compressive strength is low, the spread of flux to the joint part is poor to easily cause joining failure, and the shape is complicated to increase the machining cost.

In this flat tube for the heat exchanger, the flat tube for performing heat exchange is formed by bending both end parts of a metallic plate to form side parts, mutually opposing two thus formed plates having a U-shaped section, and mutually superposing the plates with one U-shaped section plate inserted in the inside of the other U-shaped section plate to form a passage inside. Thus, the flat tube can be simply manufactured by press working, and the working cost can be reduced by combination with simplification of a shape. The joint part can be made wider by superposing the side parts to attain excellent compressive strength, and the joint parts can be easily accessed to spread flux well so that the occurrence of joining failure can be prevented.