Supervisory control equipment for smart grids provided with a plurality of generators and loads and operated in interconnection with a commercial power system through an interconnected circuit breaker, comprising a frequency control ability calculation part for calculating the frequency control ability of the interconnected system by using a total power demand and a bus bar frequency; and an islanding and interconnection detection part for calculating frequency control ability of the commercial power system according to the frequency control ability of the system of the frequency control ability calculation part to discriminate between the interconnected and islanding operations according to the magnitude of the frequency control ability.