PURPOSE: To perform a measurement in live line by calculating, values of earth capacities and insulations to the earth for each phase based on phase voltage, line voltage, and phase difference of each face.

CONSTITUTION: The calculator 37 receives the output signals from the phase voltage meters for each phase 31, 32, the line voltage meter 34, and the phase difference meters 35, 36. The calculator 37 uses the detected values to calculate the values of earth capacities and insulation to the earth for each phase to permit the signal of calculated values to be outputted. The signals from the calculator 37 enters the display unit 38, which indicates the values normalized in, for example, equivalent resistance. The signals from the calculator 37 also enters the recorder 39, which continuously records the calculated values to indicate the variations in time.