PURPOSE: To shorten a time required for start/stop of a heat source apparatus and to realize fine load regulation.

CONSTITUTION: In the equipment for controlling flow rates of heat source apparatus water systems provided for a plurality of heat source apparatuses 20-1 and 20-2 respectively, the heat source apparatus water systems are joined into one water system between the respective water system entrances of the heat source apparatus water systems and the heat source apparatuses 20-1 and 20-2. The common water system part thus formed is connected onto the inlet side of a branching valve 25 and water systems 21b and 22b of the heat source apparatuses 20-1 and 20-2 are connected in parallel onto the outlet side of the branching valve 25. Besides, a flow dividing ratio control means which controls the branching valve 25 in accordance with start or stop of the heat source apparatuses 20-1 and 20-2 so as to change over a flow dividing ratio between the heat source apparatuses 20-1 and 20-2 is provided.