It is an object of the invention to prevent unnecessary inefficiency in a system in which a plurality of usage units that use an aqueous medium are connected to a single heat source unit. A heat source unit (2) has a capacity-variable heat source-side compressor (21) and a heat source-side heat exchanger (24) which functions as a radiator of refrigerant. Each of usage units (4a, 4b) connected to the heat source unit (2) have usage-side heat exchangers (41a, 41b) which function as evaporators of refrigerant and cool an aqueous medium. An operating capacity controller (12b) controls the capacity of the heat source-side compressor (21) so that evaporation temperature (Te) of refrigerant of each of the usage-side heat exchangers (41 a, 41 b) reaches a first target evaporation temperature (Tte1). Second target evaporation temperature calculation units (191a, 191b) calculate second target evaporation temperatures (Tte2a, Tte2b) for each of the usage units (4a, 4b), which allow the outlet temperatures of the aqueous medium in the usage-side heat exchangers (41 a, 41b) to reach set temperatures (Tsa, Tsb), and a first target evaporation temperature decision unit (12a) decides minimum value of the second target evaporation temperatures (Tte2a, Tte2b) as the first target evaporation temperature (Tte1).