An outdoor unit of an air-conditioning apparatus includes: a housing; a heat exchanger provided in the housing; an electric component box provided in the housing; and a separator that partitions the inside of the housing into a first chamber and a second chamber. The separator is provided on a front surface of the heat exchanger. The first chamber and the second chamber are provided side by side in a lateral direction as viewed in a side-on view of the outdoor unit. The electric component box is provided on the front surface of the heat exchanger and above the separator. The outdoor unit includes a first positioning member and a second positioning member. The first positioning member is provided on the electric component box, and determines the position of the electric component box in a vertical direction and a front-rear direction relative to the heat exchanger. The second positioning member is provided on a bottom surface of the electric component box, and determines the position of the electric component box in the lateral direction relative to the separator.