An outdoor unit of an air-conditioning apparatus includes a casing forming an outer shell, a terminal block disposed in the casing, a terminal block support element configured to support the terminal block, and an earth grounding plate sandwiched between the terminal block and the terminal block support element. An engaging portion to be engaged with the terminal block support element is provided in the earth grounding plate. A fixing element is provided to fasten the terminal block and the earth grounding plate engaged with the terminal block support element by the engaging portion together to the terminal block support element.