An image, which is captured by a camera that a worker, etc., carries, is once stored in a ring buffer memory for storing image signals. The image is extracted from the ring buffer memory, and a quasi-moving image is generated. In a normal state, the quasi-moving image is displayed on a monitor of a center such as a control room, etc. via codecs on transmitting and receiving sides. When a user viewing the monitor makes a request to view a sharp image of a particular frame, or the high-quality motion of a subject while viewing the frames preceding or succeeding a particular frame, the image frame or frames are read from the buffer memory for storing image signals, and displayed on the monitor.