A secondary pump-type heat source system includes: heat sources connected in parallel; a load system in which the heat source water flows; a primary pump supplying the heat source water to the load system; a secondary pump provided for each heat source and supplies the heat source water subjected to heat exchange in the load system to the heat source; and a heat source controller calculating flow quantity of the heat source water flowing in the heat source side and flow quantity of the heat source water flowing in the load system side by assigning a result from measurement by a water temperature sensor detecting heat source temperature to an operating characteristic of each heat source and controlling operation of the secondary pumps based on the calculation result.