To measure the electric parameter of a signal to be measured of which the signal waveform does not cross a reference value at low cost.

A DC component calculation section 4 calculates DC component data Ddc indicating the DC component Svd of a voltage signal Sv for each one cycle of a reference signal S1. An AC component calculation section 5 subtracts the DC component data Ddc from digital data D1 and outputs it as AC component data Dac1 indicating the AC component Sva of the voltage signal Sv. An arithmetic processing section 7 detects the timing at which the value of AC component data Dac2 after noise removal is increasing to cross the reference value and performs cycle detection processing for detecting the AC cycle of the AC component data Dac2, signal generation processing for, when the AC cycle of the AC component data Dac2 is detected, changing the cycle from an initial cycle to this AC cycle to output the reference signal S1, and parameter calculation processing for calculating the effective value Vrms of the voltage signal Sv through the digital data D1 for one cycle of the reference signal S1.