[Object] To prevent a fastening member such as a bolt from being exposed from a bottom plate when a heater is fixed to the bottom plate using a heater fixture.[Solution] An outdoor unit 100 of an air-conditioning apparatus includes a bottom plate 4, a heat exchanger 10 mounted on the bottom plate 4, and a fan 11 sending air to the heat exchanger 10. The outdoor unit 100 includes a heater 12 provided on the bottom plate 4; a fan retaining portion 20, mounted on the bottom plate 4, for retaining the fan 11; and a heater fixture 40, mounted on the fan retaining portion 20, for fixing the heater 12 by pressing the heater 12 against the bottom plate 4 from above.