A heat exchanger comprising: a plurality of fins arranged in parallel with each other and extending along upper and lower directions; and a flat tube extending crosswise to the plurality of fins, each of the plurality of fins having a first side edge portion and a second side edge portion, the first side edge portion and the second side edge portion extending along the upper and lower directions, the flat tube having end portions in the longitudinal axis direction of the flat tube in a cross-section perpendicular to the extending direction of the flat tube, the end portions comprising a first end portion and a second end portion, the first end portion being positioned closer to the first side edge portion than the second end portion is to the first side edge portion, each of the plurality of fins including at least one water guide portion formed at at least one of a position between the first side edge portion and the first end portion, and a position between the second side edge portion and the second end portion, the water guide portion extending in the upper and lower directions, a lower edge portion (10c, 10g) positioned below the flat tube in the upper and lower directions, and a protruding edge portion (10d, 10e, 10h) positioned below the water guide portion in the upper and lower directions, and protruding downwardly relative to the lower edge portion (10c, 10g), characterized in that the protruding edge portion (10d, 10e, 10h) includes: a bottom edge (10d1, 10e1) positioned at a lower end of the protruding edge portion (10d, 10e, 10h); a first side edge (10d2, 10e2) positioned between the bottom edge (10d1, 10e1) and at least one of the first side edge portion and the second side edge portion respectively; and a second side edge (10d3, 10e3) positioned between the lower edge portion (10c, 10g) and the bottom edge (10d1, 10e1), wherein the inclination of the second side edge (10d3, 10e3) relative to a horizontal plane is greater than the inclination of the lower edge portion (10c, 10g) relative to a horizontal plane, and wherein letting a width of the protruding edge portion (10d, 10e, 10h) at an upper end be W2 and a width of the water guide portion be W3, a relationship of W3 ≤ W2 is satisfied. a plurality of fins arranged in parallel with each other and extending along upper and lower directions; and a flat tube extending crosswise to the plurality of fins, each of the plurality of fins having a first side edge portion and a second side edge portion, the first side edge portion and the second side edge portion extending along the upper and lower directions, the flat tube having end portions in the longitudinal axis direction of the flat tube in a cross-section perpendicular to the extending direction of the flat tube, the end portions comprising a first end portion and a second end portion, the first end portion being positioned closer to the first side edge portion than the second end portion is to the first side edge portion, each of the plurality of fins including at least one water guide portion formed at at least one of a position between the first side edge portion and the first end portion, and a position between the second side edge portion and the second end portion, the water guide portion extending in the upper and lower directions, a lower edge portion (10c, 10g) positioned below the flat tube in the upper and lower directions, and a protruding edge portion (10d, 10e, 10h) positioned below the water guide portion in the upper and lower directions, and protruding downwardly relative to the lower edge portion (10c, 10g), characterized in that the protruding edge portion (10d, 10e, 10h) includes: a bottom edge (10d1, 10e1) positioned at a lower end of the protruding edge portion (10d, 10e, 10h); a first side edge (10d2, 10e2) positioned between the bottom edge (10d1, 10e1) and at least one of the first side edge portion and the second side edge portion respectively; and a second side edge (10d3, 10e3) positioned between the lower edge portion (10c, 10g) and the bottom edge (10d1, 10e1), wherein the inclination of the second side edge (10d3, 10e3) relative to a horizontal plane is greater than the inclination of the lower edge portion (10c, 10g) relative to a horizontal plane, and wherein letting a width of the protruding edge portion (10d, 10e, 10h) at an upper end be W2 and a width of the water guide portion be W3, a bottom edge (10d1, 10e1) positioned at a lower end of the protruding edge portion (10d, 10e, 10h); a first side edge (10d2, 10e2) positioned between the bottom edge (10d1, 10e1) and at least one of the first side edge portion and the second side edge portion respectively; and a second side edge (10d3, 10e3) positioned between the lower edge portion (10c, 10g) and the bottom edge (10d1, 10e1), wherein the inclination of the second side edge (10d3, 10e3) relative to a horizontal plane is greater than the inclination of the lower edge portion (10c, 10g) relative to a horizontal plane, and wherein letting a width of the protruding edge portion (10d, 10e, 10h) at an upper end be W2 and a width of the water guide portion be W3,