An air-conditioning apparatus (A, B), comprising: at least one outdoor unit equipped with a compressor and a heat source side heat exchanger, in which a heat source side refrigerant flows; at least one refrigerant indoor unit equipped with an expansion device and a first use side heat exchanger, in which the heat source side refrigerant supplied from the at least one outdoor unit flows; a plurality of heat medium indoor units each equipped with a second use side heat exchanger in which a heat medium different from the heat source side refrigerant flows; a first heat medium relay unit interposed between the at least one outdoor unit and the at least one refrigerant indoor unit and between the at least one outdoor unit and the heat medium indoor units, having a piping in which the heat source side refrigerant flowing from the at least one outdoor unit passes and a piping in which the heat source side refrigerant returning back to the at least one outdoor unit passes; and at least one second heat medium relay unit (3b, 110) interposed between the first heat medium relay unit and the heat medium indoor units, and including a plurality of heat exchangers related to heat medium that transfers heating energy or cooling energy, which is generated in the at least one outdoor unit and is stored in the heat source side refrigerant, to the heat medium, expansion devices for the heat source side refrigerant corresponding to the respective heat exchangers related to heat medium, heat medium sending devices, heat medium flow control devices, and first heat medium flow switching devices and second heat medium flow switching devices respectively provided to the second use side heat exchangers, each of the flow switching devices switching a passage for the heat medium flowing to the corresponding second use side heat exchanger to a passage that is in communication with each of the heat exchangers related to heat medium, wherein the heat exchangers related to heat medium, the heat medium sending devices, the first heat medium flow switching devices, the heat medium flow control devices, the use side heat exchangers, and the second heat medium flow switching devices are connected in series in turn by piping, wherein the use side heat exchangers are connected in parallel to each of the heat exchangers related to heat medium, wherein one or some of the heat exchangers related to heat medium is made to function as a condenser and one or some of the remaining heat exchangers related to heat medium is made to function as an evaporator so that the second use side heat exchangers are capable of performing cooling operation and heating operation simultaneously. at least one outdoor unit equipped with a compressor and a heat source side heat exchanger, in which a heat source side refrigerant flows; at least one refrigerant indoor unit equipped with an expansion device and a first use side heat exchanger, in which the heat source side refrigerant supplied from the at least one outdoor unit flows; a plurality of heat medium indoor units each equipped with a second use side heat exchanger in which a heat medium different from the heat source side refrigerant flows; a first heat medium relay unit interposed between the at least one outdoor unit and the at least one refrigerant indoor unit and between the at least one outdoor unit and the heat medium indoor units, having a piping in which the heat source side refrigerant flowing from the at least one outdoor unit passes and a piping in which the heat source side refrigerant returning back to the at least one outdoor unit passes; and at least one second heat medium relay unit (3b, 110) interposed between the first heat medium relay unit and the heat medium indoor units, and including a plurality of heat exchangers related to heat medium that transfers heating energy or cooling energy, which is generated in the at least one outdoor unit and is stored in the heat source side refrigerant, to the heat medium, expansion devices for the heat source side refrigerant corresponding to the respective heat exchangers related to heat medium, heat medium sending devices, heat medium flow control devices, and first heat medium flow switching devices and second heat medium flow switching devices respectively provided to the second use side heat exchangers, each of the flow switching devices switching a passage for the heat medium flowing to the corresponding second use side heat exchanger to a passage that is in communication with each of the heat exchangers related to heat medium, wherein the heat exchangers related to heat medium, the heat medium sending devices, the first heat medium flow switching devices, the heat medium flow control devices, the use side heat exchangers, and the second heat medium flow switching devices are connected in series in turn by piping, wherein the use side heat exchangers are connected in parallel to each of the heat exchangers related to heat medium, wherein one or some of the heat exchangers related to heat medium is made to function as a condenser and one or some of the remaining heat exchangers related to heat medium is made to function as an evaporator so that the second use side heat exchangers are capable of performing cooling operation and heating operation simultaneously.