PURPOSE: To make it possible to control the flow rate of cool/heat water depending a thermal load by detecting the temperature of circulating cool/hot water by a cool/hot water temperature detecting means when the thermal load increases or decreases, and judging the detected value by cool/hot water judging means thereby to increase or reduce the operational speed of a cool/hot water pump.

CONSTITUTION: Cool/hot water delivered from a cool/hot water pump has the number of cool/hot water generators 110 controlled by a cool/hot water machine two-way valve 110, cooled or heated, has its flow rate detected in a flow rate transmitter 107 and has its differential pressure detected by a differential pressure transmitter 101, discharging energees at load 102, has the number of operation controlled by a two-way valve 109 and thus circulated to the suction side of cool/hot water. By a cool/hot water sensor 105 for detecting the abrupt change of the thermal load and a controller 104 added with a function to calculate a load on the combustion state of the cool/hot water generator 101, if a differential pressure P on the load side is an acceleration zone, the cool/hot water pump 103 is accelerated and if it is in a speed reduction zone, its speed is reduced, and the speed of the cool/hot water pump 103 is controlled based on the signal of the differential pressure transmitted 108.