The present invention relates to a novel means and a novel method for detecting a capacitance connected to AC power, which detect a sensor capacitance on the basis of a charge sharing phenomenon occurring due to a difference between voltages applied to a sensor capacitor and an auxiliary capacitor connected to a detection system when an AC voltage applied to the detection system alternates. According to the present invention, since the sensitivity of a signal detected by a detection system is improved, a magnitude and a change amount of a sensor capacitance are stably acquired.