This heat exchanger comprises a flat tube, a circular tube, and a flat joint that connects the flat tube and the circular tube. The flat joint has at least two joint members obtained by dividing the same at a longitudinal section along the long side of the flat shape and at the center of the axis of the flat tube, and is formed by brazing the two joint members with the flat tube and the circular tube interposed therebetween. A first insertion port corresponding to the flat tube is formed on one end side of the flat joint and a second insertion port corresponding to the circular tube is formed on the other end side. A brazing material reservoir for collecting the molten brazing material during brazing is formed at the first insertion port-side portion of at least one of the two joint members where the flat tube is brazed. Thus, by collecting the brazing material in the brazing material reservoir provided at the portion of the flat joint where the flat tube is brazed, the brazing material can be sufficiently distributed to the joint surface where the brazing material is required during brazing, and the generation of voids due to insufficient supply of the brazing material can be suppressed.