An axial flow fan comprising: - a boss that rotates about a shaft center; and - a plurality of blades disposed in an outer peripheral portion of the boss, wherein a surface of a downstream side of each blade connects to a surface of an upstream side of the blade at an outer peripheral end of the blade, wherein the blades are each formed such that a chord centerline connecting chord center points from an inner peripheral end of the blade to an outer peripheral end of the blade is, when seen in a plane that contains the fan rotation axis and when the fan is oriented such that this rotation axis is vertical, curved so as to protrude toward a downstream side of an air flow with respect to a reference horizontal line that passes through the chord center point at the inner peripheral end of the blade, wherein the chord centerline protrudes toward the downstream side with respect to said reference line over the whole radial extension of the blade, wherein the chord centerline of each blade is divided into a first region and a second region in a range of the blade from the inner peripheral end to the outer peripheral end, wherein in the first region, the blade is formed such that the chord centerline is curved so as to be directed toward the downstream side of the air flow as the chord centerline extends toward an outer peripheral side and so as to protrude toward the downstream side with respect to said reference line, and wherein in the second region, the blade is formed such that the chord centerline is curved so as to be directed toward an upstream side of the air flow as the chord centerline extends toward the outer peripheral side and so as to protrude toward the downstream side with respect to said reference line, the axial fan being characterised in that, where Ro is a radius of a boundary between the first region and the second region, Rb is a radius of the boss, and Rt is a radius of an outer periphery of the blade, the relationship among the Ro, the Rt, and the Rb is set in a range that satisfies: 0.55 < Ro / Rt − Rb < 0.96, and further in that, where Zmax is a maximum value of a distance in a direction perpendicular to said reference line between the chord centerline and said reference line and Rt is a radius of an outer periphery of the blade, the relationship between the Zmax and the Rt is set in a range that satisfies: 0.02 < Zmax / Rt < 0.14, and in that the chord centerline of each blade is concave towards the upstream side and convex towards the downstream side over the whole radial extension of the blade. - a boss that rotates about a shaft center; and - a plurality of blades disposed in an outer peripheral portion of the boss, wherein a surface of a downstream side of each blade connects to a surface of an upstream side of the blade at an outer peripheral end of the blade, wherein the blades are each formed such that a chord centerline connecting chord center points from an inner peripheral end of the blade to an outer peripheral end of the blade is, when seen in a plane that contains the fan rotation axis and when the fan is oriented such that this rotation axis is vertical, curved so as to protrude toward a downstream side of an air flow with respect to a reference horizontal line that passes through the chord center point at the inner peripheral end of the blade, wherein the chord centerline protrudes toward the downstream side with respect to said reference line over the whole radial extension of the blade,