An indoor unit of an air-conditioning apparatus includes a base forming a rear surface and a part of a top surface of a main body and a design panel removably attached to at least one of a left side and a right side of the base to form a part of the top surface, a part of a lower surface, and a side surface of the main body. The base includes a first corner portion connecting a top surface and a side surface of the base and a lower surface and the side surface of the base and a step portion formed on at least one of the top surface and the lower surface of the base. The design panel includes a second corner portion connecting a top surface and a side surface of the design panel and a lower surface and the side surface of the design panel.