In a client-server system comprising a plurality of client terminal devices and a server device which transmits and receives information to and from the plurality of client terminal devices, the server device comprises an acquisition unit which obtains a priority of the client terminal device from a priority storage unit, based on a control request from the client terminal device, a determination unit which determines whether or not the control request is accepted, based on the obtained priority, and an execution unit which executes control in response to the control request when the determination unit determines that the control request is accepted.