PURPOSE: To correctly measure impedance by obtaining the ratio between the energy containing the wave-form distortion constituent detected from the current flowing a measured impedance element or the voltage across both ends of the element and the energy removed with the wave-form distortion constituent.

CONSTITUTION: When a measured impedance element 14 is capacitive or resistive, a selector switch 17 is connected to a current/voltage converter 16 side, a selector switch 32 is connected to the switch 17 side, and the in-phase constituent and orthogonal constituent of the current flowing in the element 14 are measured. The switch 32 is connected to a filter 31 side, and the in-phase constituent removed with the wave-form distortion constituent in the current flowing in the element 14 and the orthogonal constituent are measured. The energy P1 containing the wave-form distortion constituent of the current flowing in the element 14 and the energy P2 removed with the wave-form distortion constituent are calculated to determine the energy ratio P2/P1, if the ratio is 0.99 or below, for example, it is judged that a large quantity of the distortion constituent exists and no correct measured result is obtained, and it is displayed 25. When the element 14 is inductive, the switch 17 is connected to a differential circuit 28 side, and similar measurement is performed on the voltage difference between both ends of the element 14.