To interrupt power supply to a load automatically by delivering an abnormal attitude signal from an attitude variation detecting means to an operating means when the initial attitude of a watthour meter is varied due to a disaster, or the like, and then delivering a signal for interrupting a distribution line from the operating means to a switch.

A watthour meter 1 comprises a voltage detecting section 6 and a current detecting section 7 which detect the voltage and the current, respectively, and deliver signals to a central operating section 10. The central operating section 10 determines the electric energy from voltage and current signals being inputted and delivers a signal indivative of the electric energy to a display section 12. An attitude variation detecting section 13 detects variation of the horizontal attitude, for example, to deliver an abnormal attitude signal to the central operating section 10. Upon receiving the abnormal attitude signal, the central operating section 10 delivers a signal for opening the circuit to a switch 14 which then interrupts power supply to a load 3.