To obtain the controller for a refrigerating machine, in which mechanical lifetime can be prolonged by stabilizing the temperature of chilled water to reduce the operation of a control valve.

The controller for refrigerating machine comprises an operating section, generating an opening command signal S4 of a control valve 71 through operation by the chilled water temperature of a refrigerating machine having the control valve 71 or a set chilled water temperature, a comparison section 201 outputting an open/ close command signal S6 of the control valve, based on the comparison data with an actual opening thereof or the opening of the control valve indicated by the opening command signal, a section 202 for opening/closing the control valve, in response to the open/close command signal, and a refrigerating machine settled state deciding section 203 outputting a refrigerating machine settled signal S5, when it is deemed that the refrigerating machine has settled. Chilled water temperature of the refrigerating machine varies, depending on the opening of the control valve and the comparing section makes a decision whether the comparison data belongs to a dead band. The open/close command signal is delivered, if it belongs to a dead band, otherwise the open/close command signal is not delivered but the dead band is altered by the refrigerating machine signal.