A heat exchanger includes fins and a plurality of pairs of cut-and-raised parts. Each pair of the cut-and-raised parts are positioned on both left and right sides in a width direction on a downstream side in a heating gas flowing direction around an outer circumference surface of each of upstream pipe body parts and face a downstream part on the outer circumference surface with a first gap therebetween. A width between upstream end parts of each pair of the cut-and-raised parts is larger than an outer diameter of each of the upstream pipe body parts. In addition, each pair of the cut-and-raised parts are inclined such that a width between downstream end parts becomes smaller than the width between the upstream end parts. A heating gas passing part having a width narrower than a dimension therebetween is provided in a region between two adjacent upstream pipe body parts.