A first circulation channel connects a first heat demand part and first supply heat exchanger with its forward route and return route. Supply and discharge channels are connected to a first heat accumulation tank, which accommodates a second heat medium heated in the first supply heat exchanger and supplied via the supply channel. A heat accumulation switching valve changes over communication of the second heat medium serving as hot heat or cold heat flowing from the first supply heat exchanger and supplied to the first heat demand part without branching to the supply channel or branching to the supply channel and supplied to the first heat accumulation tank. A heat-accumulating hot-water-supplying air conditioner operates at a first temperature when the second heat medium from the first supply heat exchanger branches to the supply channel, and at a second lower temperature when the second heat medium does not branch to the supply channel.