A communication system according to the present invention includes a server and a plurality of apparatus. Each of the apparatuses controls a state of power supply to a device integrated in the apparatus in accordance with an instruction from the server. The server assigns one of a plurality of time slots that are repeated periodically to each of the apparatuses, and notifies each of the apparatuses of information indicating the assigned time slot. Each of the apparatuses, if a pre-set criterion for each of the apparatuses to turn on power supply to the device is satisfied, turns on power supply to the device when the time slot notified by the server is reached.