PURPOSE: To easily confirm the presence or absence of both the power source side applied voltage and the load side applied voltage at the time of closing a circuit breaker by providing voltage sensors for detecting both the power source side voltage and the load side voltage at two support insulators of a stationary frame, and displaying both the applied voltages.

CONSTITUTION: Two support insulators 14 are disposed in a stationary frame 13. A power source side conductor 16 and a power source side stationary contactor 15 are connected to the one insulator 14, and a load side conductor 18 and a load side stationary contactor 17 are connected to the other insulator 14. Voltage sensors 19 made of capacitors are embedded in the insulators 14. The power source side voltage and the load side voltage of the breaker 4 are detected by both the sensors 19, and when there is the applied voltage in a display circuit 21, their pilot lamps 22 are energized. As a result, at the time of closing the breaker 4, the presence or absence of both the applied voltages can be easily confirmed, and in the case of operating the breakers at the time of maintenance, safety can be improved.