An indoor unit of an air-conditioning apparatus (A), the indoor unit comprising: 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 , wherein the base includes a first corner portion connecting a top surface and a side surface of the base , and a step portion formed on the top surface of the base , wherein the design panel includes a second corner portion connecting a top surface and a side surface of the design panel , and a cutout portion formed in the top surface of the design panel , the indoor unit characterized in that when the design panel is attached to the base the step portion has a top surface portion (1a-2) exposed through the cutout portion , with the top surface portion (1a-2) and the design panel forming the top surface of the main body , and the design panel forms the side surface of the main body , with the second corner portion covering the first corner portion , and the step portion includes a wall portion (1a-1) projecting outward of an end portion of the first corner portion , and the top surface portion (1a-2) continuously extending from the wall portion (1a-1) in a width direction of the base , and when the design panel is attached to the base , the top surface portion (1a-2) and the design panel form a flat top surface of the main body . 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 , wherein the base includes a first corner portion connecting a top surface and a side surface of the base , and a step portion formed on the top surface of the base , a first corner portion connecting a top surface and a side surface of the base , and a step portion formed on the top surface of the base , wherein the design panel includes a second corner portion connecting a top surface and a side surface of the design panel , and a cutout portion formed in the top surface of the design panel , the indoor unit characterized in that a second corner portion connecting a top surface and a side surface of the design panel , and a cutout portion formed in the top surface of the design panel , the indoor unit characterized in that when the design panel is attached to the base the step portion has a top surface portion (1a-2) exposed through the cutout portion , with the top surface portion (1a-2) and the design panel forming the top surface of the main body , and the design panel forms the side surface of the main body , with the second corner portion covering the first corner portion , and the step portion includes a wall portion (1a-1) projecting outward of an end portion of the first corner portion , and the top surface portion (1a-2) continuously extending from the wall portion (1a-1) in a width direction of the base , and the step portion has a top surface portion (1a-2) exposed through the cutout portion , with the top surface portion (1a-2) and the design panel forming the top surface of the main body , and the design panel forms the side surface of the main body , with the second corner portion covering the first corner portion , and the step portion includes a wall portion (1a-1) projecting outward of an end portion of the first corner portion , and the top surface portion (1a-2) continuously extending from the wall portion (1a-1) in a width direction of the base , and when the design panel is attached to the base , the top surface portion (1a-2) and the design panel form a flat top surface of the main body . <EOS>