An indoor unit of an air-conditioning apparatus includes a suction grille having an air inlet through which air flows in, a decorative panel to which the suction grille is mounted and having an air outlet through which the air flows out, a casing to which the decorative panel is mounted and defining an air passage between the air inlet and the air outlet, a fan located to face the suction grille in the casing and configured to cause the air to flow in through the air inlet and flow out through the air outlet, a heat exchanger located in the air passage between the fan and the air outlet in the casing and configured to exchange heat between refrigerant flowing in the heat exchanger and the air, and a refrigerant detection sensor configured to detect leakage of the refrigerant.