To indicate the electric rate of individual electric apparatus by providing a microcomputer for calculating the mean values of current and voltage and multiplying the mean values by an electric rate conversion factor determining the unit conversion rate of a power company thereby calculating power consumption in terms of electric rate.

An electric plug 2 is connected with a 100 V receptacle 1 in home and the electric plug 4 of an electric apparatus to be used or measured is connected with a receptacle 3. When power is turned on for an electric apparatus connected with the receptacle 3, a current flows from the 100 V receptacle 1 through the electric plug 2, the receptacle 3, and the electric plug 4 to the electric apparatus. A metering current sensor 6 performs conversion to a current value and a metering voltage sensor 7 performs conversion to a voltage value. Rectified waveforms of the current value and the voltage value are then averaged by an averaging circuit 9 through a full-wave rectifier circuit 8. A microcomputer, 10 integrates the average current value and the average voltage value constantly, converts the integrated value into power consumption per time and multiplies the power consumption by a factor previously inputted to the microcomputer 10 thus calculating the integrated electric rate.