A conferencing system configured to make it easy to switch video data to be displayed on a shared display device. Multiple client devices are connected to a switching device directly or via a network. The output of the switching device is connected to a shared display device. Each client device outputs, to the switching device, video data used for a presentation. The switching device registers, in a queue, the order of displaying received video data on the shared display device. The registered order can be the order of receiving video data at the switching device. The content of the queue and the allocated time of each presenter can be displayed on the shared display device. The switching device switches video data to be displayed on the shared display device at a predetermined timing according to the order of the queue.