PURPOSE: To measure electric energy with high precision, by removing an error due to the leakage impedance of the secondary winding of a current transformer, and performing conversion to a current proportional to a load current.

CONSTITUTION: A main iron core 31 and an auxiliary iron core 32 have a common primary winding 33. Secondary windings 34 and 35 having the number of turns N2 and N3 respectively are provided to the main iron core 31 and auxiliary iron core 32. When N2/N3=a=2, the influence of the load impedance ZM of the secondary winding 34 on the main iron core side is compensated by equalizing feedback impedance ZF to the sum of load impedance ZL and the impedance ZM. Then, the voltage detection part 51 of an electronic watthour meter performs conversion to a signal proportional to the load voltage (v) of a feeder and outputs it, and the current detection part 52 composed of said error compensation type current transformer performs conversion to a signal proportional to a load current (i) of the feeder, and outputs it. Both signals detected by those detection parts 51 and 52 are multiplied mutually by an arithmetic part 53 to measure electric energy.