To sense accurately a large-scale earthquake which may endanger the human life, and for minor tremors, maintain the electricity systems of ordinary households, office buildings, etc., normally.

A seismo-sensor 20 is connected with an earth leakage breaker 21, and the current flowing through the breaker 21 is changed largely by closing or opening a parallel circuit when an earthquake of specified intensity breaks out so that the breaker 21 is put off. Another sensor is provided to sense vertical vibration so that the threshold sensing the vertical vibration is different from that for lateral vibration, and the breaker 21 may be shut through a logic circuit.