System and method of controlling operation of electric device

A system for controlling an electric device operation includes a plurality of electric devices managed by a consumer associated with a power system and a plurality of control devices for controlling an operation of the electric devices. The system includes an operation time calculation unit configured to calculate a start time of an operation of increasing or decreasing power received from the plurality of electric devices based on a control command for requesting an increase or decrease of power received from the power system such that the start time is different for each of the electric devices. Each of the control devices executes an operation of increasing or decreasing reception power at an operation start time different for each of the electric devices as a result of calculation of the calculation unit.