To provide the control method of operation wherein the surface temperature of a food stuff is lowered to a predetermined temperature to effect soft landing without sticking a core temperature sensor into the food stuff.

The surface temperature of the food stuff F in a cooling chamber is imaged by an infrared ray camera 12 to operate the maximum temperature θmax from an infrared ray picture element substrate 13 and apply a proportional control based on a difference between the maximum temperature θmax and a set temperature θo on a compressor and a fan whereby a cooling capacity in the chamber is regulated to obtain a predetermined surface temperature of the food stuff F and the food stuff F is retained forcibly in the condition of maintaining the cold temperature in proportional to a time for arriving at the set temperature θo and, thereafter, the finishing of the cooling is indicated.