An axial-flow fan 100 includes an impeller 10 mounted on a rotating shaft 21 of a rotary drive device 20 and a venture casing 30 surrounding an outer periphery of the impeller 10 in a radial direction and including a suction port 41 and a discharge port 42 facing each other in an axial direction of the rotating shaft 21. An inner surface of the venture casing 30 includes a suction-side slant part 31 expending the suction port 41 outward in the radial direction of the impeller 10, a linear part 32 continuing from the suction-side slant part 31 and forming an axial flow of a fluid with the impeller 10, a discharge-side slant part 34 expanding the discharge port 42 outward in the radial direction of the impeller 10, and a curved part 33 connecting the linear part 32 and the discharge-side slant part 34.