An outdoor unit comprising: a housing in which an inlet port and an outlet port are formed; a bottom plate that forms a lower surface of the housing, a top plate that forms an upper surface of the housing, and a side wall that is provided between the bottom plate and the top plate and partitions an internal space of the housing; a heat exchanger provided in a region in the housing that adjoins the inlet port; and fans (4, 5) provided in a region in the housing that adjoins the outlet port, wherein the fans (4, 5) are a first fan and a second fan that are respectively provided in an upper side and a lower side of the region in the housing that adjoins the outlet port; characterized in that, an air flow passage is provided to extend from the heat exchanger to the fans (4, 5), and is defined by the bottom plate, the top plate, and the side wall, the side wall being located beside the fans (4, 5), wherein the side wall has a side-wall upper portion, a side-wall lower portion, and a side-wall middle portion, the side-wall upper portion being located between a central axis of the first fan and the top plate in a direction along a height of the housing, the side-wall lower portion being located between a central axis of the second fan and the bottom plate in the direction along the height of the housing, the side-wall middle portion being located between the side-wall upper portion and the side-wall lower portion, wherein cross sections of the air flow passage that are taken along a direction parallel to the bottom plate and are located between a plane through central axes of the fans (4, 5) and the side wall have respective cross-sectional areas A, B, and C such that the cross-sectional area B < the cross-sectional area A < the cross-sectional area C is satisfied, where the cross-sectional area A is any one of cross-sectional areas of a region of the flow passage that is changed in shape by the side-wall upper portion, the cross-sectional area B is any one of cross-sectional areas of a region of the flow passage that is changed in shape by the side-wall lower portion, and the cross-sectional area C is any one of cross-sectional areas of a region of the flow passage that is changed in shape by the side-wall middle portion. a housing in which an inlet port and an outlet port are formed; a bottom plate that forms a lower surface of the housing, a top plate that forms an upper surface of the housing, and a side wall that is provided between the bottom plate and the top plate and partitions an internal space of the housing; a heat exchanger provided in a region in the housing that adjoins the inlet port; and fans (4, 5) provided in a region in the housing that adjoins the outlet port, wherein the fans (4, 5) are a first fan and a second fan that are respectively provided in an upper side and a lower side of the region in the housing that adjoins the outlet port; characterized in that, an air flow passage is provided to extend from the heat exchanger to the fans (4, 5), and is defined by the bottom plate, the top plate, and the side wall, the side wall being located beside the fans (4, 5), wherein the side wall has a side-wall upper portion, a side-wall lower portion, and a side-wall middle portion, the side-wall upper portion being located between a central axis of the first fan and the top plate in a direction along a height of the housing, the side-wall lower portion being located between a central axis of the second fan and the bottom plate in the direction along the height of the housing, the side-wall middle portion being located between the side-wall upper portion and the side-wall lower portion, wherein cross sections of the air flow passage that are taken along a direction parallel to the bottom plate and are located between a plane through central axes of the fans (4, 5) and the side wall have respective cross-sectional areas A, B, and C such that the cross-sectional area B < the cross-sectional area A < the cross-sectional area C is satisfied, where the cross-sectional area A is any one of cross-sectional areas of a region of the flow passage that is changed in shape by the side-wall upper portion, the cross-sectional area B is any one of cross-sectional areas of a region of the flow passage that is changed in shape by the side-wall lower portion, and the cross-sectional area C is any one of cross-sectional areas of a region of the flow passage that is changed in shape by the side-wall middle portion.