To obviously display guard states of all picture transmission devices managed by a picture center device.

A matrix is displayed in a prescribed area on the screen of a monitor of the picture center device. Individual squares of this matrix correspond to recognition numbers of picture transmission devices managed by the picture center device respectively. The display color of each square corresponds to the current guard state of the corresponding picture transmission device. When new guard information is reported from a picture transmission device, the display color of the square corresponding to this picture transmission device in the matrix is changed to a color corresponding to this received guard information.