Indoor system and indoor unit of air-conditioning apparatus

An indoor unit of an air-conditioning apparatus, comprising:

• a main body including a main board that is provided with a control terminal compatible with a plurality of expansion components,
• wherein the main board
• is directly connected to an expansion board provided with at least one expansion terminal that is a connection terminal compliant with the same standard as the control terminal, and
• is indirectly connected to at least one of the plurality of expansion components via the expansion board,
• wherein in a case where one of the plurality of expansion components, excluding the at least one of the plurality of expansion components, includes the expansion board,
• a wiring line extending from the expansion board is connected to the control terminal, and
• a wiring line extending from the at least one of the plurality of expansion components that includes no expansion board is connected to the at least one expansion terminal,
• whereby the main board is connected to the at least one of the plurality of expansion components that includes no expansion board via the expansion board,
• wherein in the at least one of the plurality of expansion components that includes no expansion board, a standard board configured to fulfill a standard function of the at least one of the plurality of expansion components that includes no expansion board is provided, and
• wherein the main board includes a power supply circuit configured to supply power to the expansion board directly connected to the main board and
• each of the at least one expansion component indirectly connected to the main board.