A heat exchanger comprising: a plate-shaped fin having a width; and a heat transfer tube arranged to penetrate the fin, the fin having a first end portion and a second end portion opposed to each other with the width being interposed, in a direction of the width of the fin, a first region where the heat transfer tube is arranged, a second region arranged on a side of the first end portion relative to the first region, and a third region arranged on a side of the second end portion relative to the first region being located, characterised in that the heat transfer tube comprises an outer wall lower surface located along the direction of the width, a first outer wall upper surface inclined at a first angle of inclination with respect to the outer wall lower surface from the side of the first end portion toward the second end portion as being away from the outer wall lower surface, a second outer wall upper surface inclined at a second angle of inclination, greater than the first angle of inclination, with respect to the outer wall lower surface, from the first outer wall upper surface toward the second end portion as being closer to the outer wall lower surface and connected to the outer wall lower surface, a first rounded heat transfer tube end portion connected to the outer wall lower surface and the first outer wall upper surface, a second rounded heat transfer tube end portion connected to the first outer wall upper surface and the second outer wall upper surface, and a third rounded heat transfer tube end portion connected to the outer wall lower surface and the second outer wall upper surface. a plate-shaped fin having a width; and a heat transfer tube arranged to penetrate the fin, the fin having a first end portion and a second end portion opposed to each other with the width being interposed, in a direction of the width of the fin, a first region where the heat transfer tube is arranged, a second region arranged on a side of the first end portion relative to the first region, and a third region arranged on a side of the second end portion relative to the first region being located, a first region where the heat transfer tube is arranged, a second region arranged on a side of the first end portion relative to the first region, and a third region arranged on a side of the second end portion relative to the first region being located, characterised in that the heat transfer tube comprises an outer wall lower surface located along the direction of the width, a first outer wall upper surface inclined at a first angle of inclination with respect to the outer wall lower surface from the side of the first end portion toward the second end portion as being away from the outer wall lower surface, a second outer wall upper surface inclined at a second angle of inclination, greater than the first angle of inclination, with respect to the outer wall lower surface, from the first outer wall upper surface toward the second end portion as being closer to the outer wall lower surface and connected to the outer wall lower surface, a first rounded heat transfer tube end portion connected to the outer wall lower surface and the first outer wall upper surface, a second rounded heat transfer tube end portion connected to the first outer wall upper surface and the second outer wall upper surface, and a third rounded heat transfer tube end portion connected to the outer wall lower surface and the second outer wall upper surface. an outer wall lower surface located along the direction of the width, a first outer wall upper surface inclined at a first angle of inclination with respect to the outer wall lower surface from the side of the first end portion toward the second end portion as being away from the outer wall lower surface, a second outer wall upper surface inclined at a second angle of inclination, greater than the first angle of inclination, with respect to the outer wall lower surface, from the first outer wall upper surface toward the second end portion as being closer to the outer wall lower surface and connected to the outer wall lower surface, a first rounded heat transfer tube end portion connected to the outer wall lower surface and the first outer wall upper surface, a second rounded heat transfer tube end portion connected to the first outer wall upper surface and the second outer wall upper surface, and a third rounded heat transfer tube end portion connected to the outer wall lower surface and the second outer wall upper surface.