A heat source apparatus of a heat source system made up of a heat source machine side and a load facility side includes a heat source machine, and a heat source controller, wherein the heat source machine includes: a water heat exchanger that exchanges heat between heat source water and a refrigerant circulating through a refrigeration cycle; a primary pump that delivers heat source water to the water heat exchanger; and a heat source machine control device that operates based on information from the water heat exchanger and the primary pump, and wherein the heat source controller is connected to the heat source machine control device on a heat source side and to the load facility side so as to determine, after the primary pump is activated, whether or not the heat source water is normally fed by the primary pump based on a temperature difference between the heat source water before and after the water heat exchanger or a pressure difference between the heat source water before and after the water heat exchanger, and so as to then operate the refrigeration cycle after water feed is confirmed through water feed determination.