An air-conditioning-apparatus outdoor unit includes a casing, an air-sending device chamber, a machine chamber, a partition, a heat exchanger cover, and an electric box including a bottom plate that defines a bottom surface of the electric box and that is joined to an upper end of the heat exchanger cover. The casing includes a shell panel having an outdoor-air inlet that is open. The heat exchanger cover is positioned to face the outdoor-air inlet, and defines, together with the partition and the shell panel, an air passage communicating with the outdoor-air inlet in the machine chamber. The bottom plate of the electric box has a bottom opening communicating with the air passage.