PURPOSE: To improve the precision of measurement of electric energy by making electric power information linear by detecting ambient temperature and by removing a temperature fluctuation component and a nonlinear component that the electric power information has on the basis of the temperature information.

CONSTITUTION: Light beams from light emitting diodes 20a and 21a of the 1st and 2nd photocouplers 20 and 21 of a voltage detector 7 are received by photodiodes 20b and 21b, whose voltage signals are sent to a multiplier 9. According to the variation of the consumption of a current (i), the intensity H of a magnetic field established by the magnetic cor 26 of a current detector 8 varies, and resistance values 28a and 28b of a magnetic resistance element 28 vary correspondingly and are converted into electric signals, which are sent from an amplifier 29 to the multiplier 9. The result of the multiplier 9 is temperature calibrated by the output voltage signal VT of a temperature converter 10 proportional to the temperature T of a temperature sensor 11 to eliminate nonlinear characteristics and temperature fluctuation characteristics, thereby making a digital signal, having electric power information, linear. It is counted by a counter to measure electric energy precisely by a small-sized and lightweight device.