Abstract: An air conditioner includes a means for detecting a frequency for controlling an AC motor of a compressor, a means for determining whether the frequency during operation converges to within a predetermined range, of the frequency required to maintain the designated temperature, and a means for shifting the designated temperature by a predetermined temperature when the frequency converges to the predetermined range. The temperature is shifted when the frequency decreases and converges to the predetermined range while the air conditioner operation causes the room temperature to approach the designated temperature. Thus, even if the body temperature of a user decreases because, for example, he is sleeping, the stable state of the operation can be accurately determined and thereby a comfortable temperature is maintained.

Abstract: An inverter apparatus comprises a bridge circuit composed of a combination of a plurality of switching transistors and a microprocessor controlling turning on and turning off of these switching transistors. Patterns of combinations of ON and OFF states of respective switching transistors obtained based on the theory of PWM (pulse width modulation) are stored in a first ROM of microprocessor. Transition of the pattern for each range of 0.degree.-30.degree. in electrical angle is stored in a second ROM in the sequence of periods subdivided from the range. Data of the time during which the pattern to be held for each period is stored in a third ROM. The microprocessor sets the holding time data in a timer, and also outputs the ON/OFF pattern, thereby turning on or turning off of each switching transistor is controlled in accordance with the count of this timer and the ON/OFF pattern. By repeating this cycle, a switching signal which continues during one cycle of AC (range of 0.degree.-360.degree.