To provide an open-circuit operating circuit of a load switch, capable of preventing damage caused by an overcurrent open circuit, for especially preventing damages, using a simple configuration without changing a hardware structure of the load switch itself.

When no overcurrent runs through, a switching auxiliary contact 8 of a main transformer breaker 1 is closed. If phase interruption is detected by a load switch phase interruption detection circuit 6 under the condition, a load switch opening command relay 47T is energized to deliver a load switch opening command, and a load switch 3 performs original commitment as an open circuit. If overcurrent runs there through, the switching auxiliary contact 8 is opened, and even if the phase interruption is detected, the load switch opening command relay 47T will not be energized and the load switch 3 will not be shifted to open-circuit operation, thus preventing damages caused by overcurrent open-circuit operation.