An air-conditioning apparatus (1, 101) comprising: a refrigerant cycle circuit having a compressor, a heat source-side heat exchanger, an expansion device (32a, 32b), and a refrigerant-side passage of a first intermediate heat exchanger (31a, 31b) connected by a refrigerant pipe to circulate refrigerant through the refrigerant cycle circuit; a heat medium cycle circuit having a heat medium-side passage of the first intermediate heat exchanger (31a, 31b) and a use-side heat exchanger (21a, 21b, 21c) connected by a heat medium pipe to circulate a heat medium through the heat medium cycle circuit; a heat storage reservoir (40, 140) including a heat storage tank to store the heat medium; a controller configured to control the compressor and the expansion device (32a, 32b); a heat medium temperature sensor (38a, 38b, 38c, 38d) configured to detect a temperature of the heat medium flowing from the first intermediate heat exchanger (31a, 31b); an indoor temperature sensor (22a, 22b, 22c) configured to detect a temperature of a space provided with the use-side heat exchanger (21a, 21b, 21c); and a tank temperature sensor configured to detect a temperature of the heat medium in the heat storage tank, wherein the first intermediate heat exchanger (31a, 31b) is configured to exchange heat between the refrigerant and the heat medium, wherein the heat medium cycle circuit includes a heat medium flow switching device (36a, 36b) configured to switch a passage to connect the heat storage reservoir (40, 140) to the heat medium cycle circuit and allow the heat medium to flow into and from the heat storage tank, wherein the controller is configured to cause the heat medium flow switching device (36a, 36b) to switch the passage based on the temperature detected by the heat medium temperature sensor (38a, 38b, 38c, 38d), the temperature detected by the indoor temperature sensor (22a, 22b, 22c), and the temperature detected by the tank temperature sensor, and wherein when the heat medium flow switching device (36a, 36b) switches the passage to connect the heat storage reservoir (40, 140) to the heat medium cycle circuit, the heat medium that exchanged heat in the first intermediate heat exchanger (31a, 31b) flows into the heat storage reservoir (40, 140) to allow the heat storage reservoir (40, 140) to store heat. a refrigerant cycle circuit having a compressor, a heat source-side heat exchanger, an expansion device (32a, 32b), and a refrigerant-side passage of a first intermediate heat exchanger (31a, 31b) connected by a refrigerant pipe to circulate refrigerant through the refrigerant cycle circuit; a heat medium cycle circuit having a heat medium-side passage of the first intermediate heat exchanger (31a, 31b) and a use-side heat exchanger (21a, 21b, 21c) connected by a heat medium pipe to circulate a heat medium through the heat medium cycle circuit; a heat storage reservoir (40, 140) including a heat storage tank to store the heat medium; a controller configured to control the compressor and the expansion device (32a, 32b); a heat medium temperature sensor (38a, 38b, 38c, 38d) configured to detect a temperature of the heat medium flowing from the first intermediate heat exchanger (31a, 31b); an indoor temperature sensor (22a, 22b, 22c) configured to detect a temperature of a space provided with the use-side heat exchanger (21a, 21b, 21c); and a tank temperature sensor configured to detect a temperature of the heat medium in the heat storage tank, wherein the first intermediate heat exchanger (31a, 31b) is configured to exchange heat between the refrigerant and the heat medium, wherein the heat medium cycle circuit includes a heat medium flow switching device (36a, 36b) configured to switch a passage to connect the heat storage reservoir (40, 140) to the heat medium cycle circuit and allow the heat medium to flow into and from the heat storage tank, wherein the controller is configured to cause the heat medium flow switching device (36a, 36b) to switch the passage based on the temperature detected by the heat medium temperature sensor (38a, 38b, 38c, 38d), the temperature detected by the indoor temperature sensor (22a, 22b, 22c), and the temperature detected by the tank temperature sensor, and wherein when the heat medium flow switching device (36a, 36b) switches the passage to connect the heat storage reservoir (40, 140) to the heat medium cycle circuit, the heat medium that exchanged heat in the first intermediate heat exchanger (31a, 31b) flows into the heat storage reservoir (40, 140) to allow the heat storage reservoir (40, 140) to store heat.