A function of being controlled by a second monitor camera controller is added to a first monitor camera controller which controls a plurality of monitor cameras. The second monitor camera controller is caused to recognize the first monitor camera controller as a monitor camera. The first monitor camera controller synthesizes videos from the monitor cameras as one video, and transmits the synthetic video to the second monitor camera controller. Control of the monitor cameras or acquisition of videos is conducted by controlling the first monitor camera controller recognized as a monitor camera by use of a control function of a part or all of pan, tilt and zoom.