An air conditioning system of enhanced cooling and heating capability, allowing finer control for suppressing generation of higher harmonics with relatively simple and generally inexpensive structure is equipped with a refrigerating cycle system (20) in which an electric motor (18) operatively coupled to the compressor (25) is driven through inverter control (8, 12) after converting AC power supplied from an AC power source (1) into a DC power. The system has a switching element (3) disposed in parallel with a DC power source for supplying a DC power derived by rectifying the AC power supplied from the AC power source (1), a DC voltage detecting circuit (10) for detecting a DC voltage (Vdc) derived by the rectification, and a PWM control circuit (11) for controlling the switching element (3) through a PWM control on the basis of a value of the DC voltage (Vdc) detected by the DC voltage detecting circuit (10).