The present invention suppresses pooling of a refrigerant or a freezer oil in low-pressure gas connection piping. A refrigeration cycle system (1) comprises: a heat source unit (2) having a heat source circuit (12) that includes a secondary-side compressor (21), a cascade heat exchanger (35), a secondary-side switching mechanism (22) for switching a flow path positioned between discharge piping (24) and the cascade heat exchanger (35), and an inlet flow path (23); a plurality of usage units (3a, 3b, 3c) each having a usage circuit (13a, 13b, 13c) that includes a usage-side heat exchanger (52a, 52b, 52c); a third interconnection pipe (7); fourth heat source piping (26); fifth heat source piping (27); a first interconnection pipe (8); first heat source piping (28); a second interconnection pipe (9); and second heat source piping (29). The heat source unit (2) has an opening/closing control valve (47) provided to the second heat source piping (29).