A refrigeration cycle apparatus comprising: a plurality of refrigeration cycles (2a-2d) allowing refrigerant to circulate therein, each of the refrigeration cycles (2a-2d) comprising a compressor (3a-3d), a refrigerant flow switching device (4a-4d), an air-side heat exchanger (5a-5d), a pressure reducing device (7a-7d), and a heat medium-side heat exchanger (8a-8d) connected in sequence with refrigerant pipes, the heat medium-side heat exchangers (8a-8d) allowing a heat medium and the refrigerant to exchange heat with each other; a heat medium of a first heat medium-side heat exchanger and a heat medium inlet of a third heat medium-side heat exchanger being connected in series with a first heat medium passage, a heat medium of a second heat medium-side heat exchanger and a heat medium inlet of a fourth heat medium-side heat exchanger being connected in series with a second heat medium passage, the first heat medium passage and the second heat medium passage being connected in parallel, wherein heat medium inlets of the first heat medium-side heat exchanger and the second heat medium-side heat exchanger being connected in parallel with a first pipe and wherein heat medium outlets of the third heat medium-side heat exchanger and the fourth heat medium-side heat exchanger being connected in parallel with a second pipe, a heat medium outlet of the first heat medium-side heat exchanger and the heat medium inlet of the second heat medium-side heat exchanger being connected in series with a third pipe, the heat medium outlet of the fourth heat medium-side heat exchanger and a heat medium inlet of the third heat medium-side heat exchanger being connected in series with a fourth pipe, the first pipe having a first bifurcation from which the first pipe branches into the first heat medium-side heat exchanger and the second heat medium-side heat exchanger, the first pipe being provided with a first valve between the first bifurcation and the heat medium inlet of the second heat medium-side heat exchanger, the second pipe having a second bifurcation from which the second pipe branches into the third heat medium-side heat exchanger and the fourth heat medium-side heat exchanger, the second pipe being provided with a second valve between the second bifurcation 13b and the heat medium outlet of the fourth heat medium-side heat exchanger, and the third pipe, the fourth pipe, and the first heat medium passages being provided with a third valve, a fourth valve, and a fifth valve, respectively. a plurality of refrigeration cycles (2a-2d) allowing refrigerant to circulate therein, each of the refrigeration cycles (2a-2d) comprising a compressor (3a-3d), a refrigerant flow switching device (4a-4d), an air-side heat exchanger (5a-5d), a pressure reducing device (7a-7d), and a heat medium-side heat exchanger (8a-8d) connected in sequence with refrigerant pipes, the heat medium-side heat exchangers (8a-8d) allowing a heat medium and the refrigerant to exchange heat with each other; a heat medium of a first heat medium-side heat exchanger and a heat medium inlet of a third heat medium-side heat exchanger being connected in series with a first heat medium passage, a heat medium of a second heat medium-side heat exchanger and a heat medium inlet of a fourth heat medium-side heat exchanger being connected in series with a second heat medium passage, the first heat medium passage and the second heat medium passage being connected in parallel, wherein heat medium inlets of the first heat medium-side heat exchanger and the second heat medium-side heat exchanger being connected in parallel with a first pipe and wherein heat medium outlets of the third heat medium-side heat exchanger and the fourth heat medium-side heat exchanger being connected in parallel with a second pipe, a heat medium outlet of the first heat medium-side heat exchanger and the heat medium inlet of the second heat medium-side heat exchanger being connected in series with a third pipe, the heat medium outlet of the fourth heat medium-side heat exchanger and a heat medium inlet of the third heat medium-side heat exchanger being connected in series with a fourth pipe, the first pipe having a first bifurcation from which the first pipe branches into the first heat medium-side heat exchanger and the second heat medium-side heat exchanger, the first pipe being provided with a first valve between the first bifurcation and the heat medium inlet of the second heat medium-side heat exchanger, the second pipe having a second bifurcation from which the second pipe branches into the third heat medium-side heat exchanger and the fourth heat medium-side heat exchanger, the second pipe being provided with a second valve between the second bifurcation 13b and the heat medium outlet of the fourth heat medium-side heat exchanger, and the third pipe, the fourth pipe, and the first heat medium passages being provided with a third valve, a fourth valve, and a fifth valve, respectively.