PURPOSE: To enable an inexpensive, comfortable and energy-saving air conditioner to be controlled by a method wherein variations in the mean value of a room temperature at each of hours in one day are determined, a temperature higher than the determined temperature by a predetermined temperature in the case of a cooling operation and a temperature lower than the determined temperature by a predetermined temperature in the case of a heating operation are set as a preset temperature for a preliminary operation during the stopping of the air conditioner, and a blower, a compressor, etc., are thereby controlled.

CONSTITUTION: In a controlling device for an air conditioner, which comprises a room temperature detector 3, a room temperature regulator 8, a control section 1 and output sections 4 and 5, variations in the mean value of a room temperature TR at each of hours in one day during a certain sample period are determined. A temperature that is higher than the determined temperature by a predetermined temperature when a cooling operation is carried out, and a temperature that is lower than the determined temperature by a predetermined temperature when a heating operation is carried out, are set as a preset temperature TS for a preliminary operation during the stopping of the air conditioner, and a signal for the preset temperature TS is outputted and, according to this output, a blower, a compressor, etc., are controlled. If the operation rate of the preliminary operation is heightened in advance prior to the time of high probability of the operation in a day, a preset temperature can be reached quickly when a user turns ON an operation switch 2. Further, the reduction of the start, time of the operation and the energy-saving operation can be simultaneously realized by changing the preset temperature at the time of the preliminary operation.