To provide a circuit breaker with a single-phase three-wire neutral line phase interruption protection, which circuit breaker does not operate to break circuit connection when a power meter is replaced so that a power supply to a load is not left disconnected when a power meter of an empty house is replaced, does not require a change in a circuit configuration, and does not cause a component cost increase.

According to the circuit breaker 1 with single-phase three-wire neutral line phase interruption protection, an X-Y phase voltage and a Y-N phase voltage on a single-phase three-wire electric path are monitored by an abnormal voltage detecting circuit 9. When the X-Y phase voltage or the Y-N phase voltage becomes an excessive voltage because of neutral line interruption, the abnormal voltage detecting circuit 9 detects the excessive voltage to break connection to a main circuit 4. The resistance of a current limiting resistor R3 is increased on a power supply path through which power is supplied from an X-Y phase to the abnormal voltage detecting circuit 9, so that a voltage in an area where a reference voltage for phase interruption detection drops when an X-Y phase voltage drops is limited to a voltage within a range of 110 to 160 V and is input to the abnormal voltage detecting circuit 9.