An air-conditioning apparatus, comprising: a refrigeration cycle device constituted by a refrigerant circuit, the refrigerant circuit being connected by piping including a compressor that compresses a refrigerant, a refrigerant flow switching device that switches a circulation path of the refrigerant, a heat source side heat exchanger for exchanging heat with the refrigerant, a plurality of heat exchangers related to heat medium (15a, 15b) each heating or cooling a heat medium different to the refrigerant by heat exchange with the refrigerant, and a plurality of expansion devices (16a, 16b) each controlling a flow rate of the refrigerant flowing in each heat exchanger related to heat medium (15a, 15b) by pressure control; a heat medium side device constituted by a heat medium circuit, the heat medium circuit being connected by piping including the heat exchangers related to heat medium (15a, 15b), a heat medium delivery device (21a, 21b) for circulating the heat medium pertaining to heat exchange of the heat exchangers related to heat medium (15a, 15b), and a use side heat exchanger (26a to 26d) exchanging heat between the heat medium and air related to a conditioned space; heat medium flow switching devices (22a to 22d, 23a to 23d) disposed on an inflow side and an outflow side of the heat medium of the use side heat exchanger (26a to 26d) in the heat medium circuit, the heat medium flow switching devices merging or diverging the heat medium by setting opening areas that are in communication with the heat exchangers related to heat medium (15a, 15b) at arbitrary degrees by control of opening degrees thereof; and a controller that controls an opening, which controls the amount of heat exchange of each of the heat exchangers related to heat medium (15a, 15b), of at least the heat medium flow switching device on an inflow side or an outflow side, during a cooling only operation mode in which all of the heat exchangers related to heat medium (15a, 15b) performs cooling and during a heating only operation mode in which all of the heat exchangers related to heat medium (15a, 15b) performs heating, characterized in that a control cycle of the heat medium flow switching devices (22a to 22d, 23a to 23d) is longer than a control cycle of the expansion devices (16a, 16b). a refrigeration cycle device constituted by a refrigerant circuit, the refrigerant circuit being connected by piping including a compressor that compresses a refrigerant, a refrigerant flow switching device that switches a circulation path of the refrigerant, a heat source side heat exchanger for exchanging heat with the refrigerant, a plurality of heat exchangers related to heat medium (15a, 15b) each heating or cooling a heat medium different to the refrigerant by heat exchange with the refrigerant, and a plurality of expansion devices (16a, 16b) each controlling a flow rate of the refrigerant flowing in each heat exchanger related to heat medium (15a, 15b) by pressure control; a heat medium side device constituted by a heat medium circuit, the heat medium circuit being connected by piping including the heat exchangers related to heat medium (15a, 15b), a heat medium delivery device (21a, 21b) for circulating the heat medium pertaining to heat exchange of the heat exchangers related to heat medium (15a, 15b), and a use side heat exchanger (26a to 26d) exchanging heat between the heat medium and air related to a conditioned space; heat medium flow switching devices (22a to 22d, 23a to 23d) disposed on an inflow side and an outflow side of the heat medium of the use side heat exchanger (26a to 26d) in the heat medium circuit, the heat medium flow switching devices merging or diverging the heat medium by setting opening areas that are in communication with the heat exchangers related to heat medium (15a, 15b) at arbitrary degrees by control of opening degrees thereof; and a controller that controls an opening, which controls the amount of heat exchange of each of the heat exchangers related to heat medium (15a, 15b), of at least the heat medium flow switching device on an inflow side or an outflow side, during a cooling only operation mode in which all of the heat exchangers related to heat medium (15a, 15b) performs cooling and during a heating only operation mode in which all of the heat exchangers related to heat medium (15a, 15b) performs heating, characterized in that a control cycle of the heat medium flow switching devices (22a to 22d, 23a to 23d) is longer than a control cycle of the expansion devices (16a, 16b).