The need for manual adjustment of a number-of-devices controller when a system is installed or when a new heat source device is added is eliminated, and operation with a high coefficient of performance is possible even when the temperature of a heat-source medium changes. A heat source system (1) includes a plurality of heat source devices (3) that are used as hot-water heat pumps and are connected in parallel with each other, heat-source-device controllers (9) provided for the respective heat source devices (3), and a number-of-devices controller (10) that allocates a hot-water load corresponding to a demand hot-water load to each heat source device (3). Each heat-source-device controller (9) transmits, to the number-of-devices controller (10), a maximum hot-water load that can be handled in the current operating condition, including the temperature of heat-source water, and heat-source-device information indicating an optimal operating range, which is a load range in which a COP of the corresponding heat source device (3) to be controlled becomes higher than or equal to a predetermined value. Then, the number-of-devices controller (10) controls the number of operated devices and performs the hot-water-load allocation based on the heat-source-device information transmitted from each heat-source-device controller (9) so that the corresponding heat source device (3) operates within the optimal operating range.