There are provided a plurality of use-side heat exchangers, inter-heat-medium heat exchangers, heat medium flow path switching devices, which switch flow paths, and pumps, which feed heat media to these paths; the inter-heat-medium heat exchangers heat or cool a heat medium by exchanging heat between the heat medium and a heat source fluid fed from a heat source apparatus. About half of the plurality of use-side heat exchangers are preheated or precooled, and the remaining use-side heat exchangers which are not preheated or precooled exchange heat media with use-side heat exchangers that have been preheated or precooled and that are not yet started to operate, suppressing energy consumed for preheating or precooling.