The present invention includes a plurality of image forming apparatuses connected to a network, and a server which controls the operation state of the image forming apparatuses via the network. The image forming apparatuses are operable in a normal operation mode and in one of plural power-saving modes with different power consumption. The server individually sets the operation mode of the image forming apparatuses in accordance with a preset power-saving operation policy, and controls the image forming apparatuses so that each of the image forming apparatuses operates in the preset operation mode in each predetermined time band.