A heat transfer tube of a heat exchanger is provided with a first and a second annular convex portions of which outer diameters are partially expanded. The first annular convex portion is positioned on an inner face side of a side plate portion of a case of the heat exchanger and is engaged with a circumferential edge portion of a first hole portion provided for the side plate portion, or the first annular convex portion contacts under pressure with an inner circumferential face of the first hole portion. The second annular convex portion is positioned on an outer face side of a header constituting member and is engaged with a circumferential edge portion of a second hole portion. Thus the side plate portion, the heat transfer tube, and a header are relatively fixed by a simple means.