PURPOSE: To enable an abnormal state to be processed at a pre-stage of occurrence of an alarm by a method wherein an estimated time ranging from a sensing time until cooling liquid reaches an alarm informing temperature is calculated in reference to a product of a ratio between an emergency control deviation of sensing temperatures and a temperature variation amount of each of the sensed temperatures at a sensing period and the sensing period.

CONSTITUTION: A temperature of cooling liquid contained within a cooling tank 1 is detected by a temperature sensing and supplying part 2. Under a normal condition, a cooling device 3 is controlled to be driven in such a way that the detected temperature becomes a predetermined monitoring temperature, for example, -30°C, and the detected temperatures are displayed in sequence at a temperature displaying part 9. In turn, a calculation part 7 takes an alarm temperature from an alarm temperature setting circuit 6, takes the detected temperatures for every detected period in reference to a timer 5 and calculates an estimated time. With such an arrangement as an emergency controlled deviation caused by a result of calculation becomes 5°C or lower due to a trouble in the cooling device 3, the estimated times are displayed in sequence at an alarm estimated time displaying part 8.