To achieve peak cut of power usage, by preventing rapid increase in the load of a refrigerating machine reliably.

In a demand controller for acquiring a varying power usage from a power monitoring device, and acquiring an operation results including operation parameters from a refrigerating machine, the refrigerating machine is instructed to operate with the operation parameters during normal operation obtained from the operation results of the refrigerating machine, when a demand alarm is generated (step S6: Yes), based on the power usage acquired from the power monitoring device. The refrigerating machine 3 is operated with the operation parameters during normal operation until the demand alarm is cancelled, and control of the refrigerating machine 3 is fixed (step S12). Consequently, the demand controller prevents rapid increase in the load of the refrigerating machine 3 reliably, thus achieving peak cut of power usage.