Abstract: In a method of calculating an electric power by digitalizing a voltage signal and a current signal of an electronic watt-hour meter and multiplying digitalized signals, precision of an electric power calculation is improved by a circuit arrangement suitable for use in an IC mainly composed of a digital circuit with a small analog scale. A voltage signal and a current signal are inputted into analog to digital conversion means composed of a sigma-delta modulation circuit and the like, respectively, and a moving average of outputs from the analog to digital conversion means is determined by moving average processing means as a low-pass filter and then voltages are multiplied by currents. An analog scale for sigma-delta modification is small. Additionally, the circuit arrangement is reduced by the employment of the low-pass filter due to the use of the moving average. Further, an electric power can be calculated with a high precision.