To detect an isolated operation of a dispersed power supply inexpensively without influencing a distribution system.

A system for detecting an isolated operation of a dispersed power supply includes: a signal injection apparatus that, in a distributing substation for supplying power from a secondary side of a power transformer to a distribution line via a first breaker, has a first voltage transformer for transforming an injection signal synchronized with a predetermined phase of a commercial power supply for injection into a secondary zero phase circuit of the power transformer; and a signal detection apparatus that, in consumer equipment having the dispersed power supply connected to the distribution line via a second breaker, has a second voltage transformer for detecting a zero phase voltage on the distribution line and detects a component of the injection signal included in the zero phase voltage.