PURPOSE: To provide a multiplier which can effectively obtain both an effective electric power and an apparent electric power with the use of a simple construction using three sguaring circuits and which can be used as a watt meter to a satisfactory extent.

CONSTITUTION: The outputs of a voltage detector 1 and a current detector 2, which are connected with the power source line of a load supply power, are introduced into the multipliers 3 and 4 according to the present invention so as to generate an effective power vi and an apparent power VI. More specifically, the first and second input signals of voltage and current components are squared by first and second squaring circuits 11 and 12 and are fed to the multiplier 4 and further to a first adder 13 so that they are added. On the other hand, the first and second input signals are added by second adders 14 and are fed to third squaring circuits 15. Third adders 16 subtract the output of the first adders 13 from the outputs of the third squaring circuit 15. Coefficient devices 17 multiply the resultant outputs with a preset coefficient so that an effective power vi is generated. The output signals of the squaring circuits 11 and 12 are fed through filters 5 and 6 to the similar multiplier 4 to generate an apparent power VI