A tube for a heat exchanger is constructed of a single plate having one end portion and the other end portion in a width direction perpendicular to a tube longitudinal direction. The single plate having opposite first and second wall surfaces is bent to have a protruding portion at a position adjacent to the one end portion in the width direction and a contact portion adjacent to the protruding portion in the width direction. The protruding portion is configured to continuously extend in the longitudinal direction and to have a protruding tip on a side of the first wall surface, and the protruding tip contacts the first wall surface of a portion along the longitudinal direction. The second wall surface at the one end portion and the contact portion contacts the first wall surface at the other end portion and a position near the other end portion, respectively.