A mobile body photographs an image with a camera while moving, and transmits to a control apparatus image data representing the photographed image and state information indicating the state thereof including the location thereof. The control apparatus displays a map including a moving range of the mobile body on a display unit and overlays a route of the mobile body on the map to display the route. The control apparatus detects an occurrence of an event such as finding of an intruder and the location of the mobile body at the time of the occurrence of the event, based on the received image data and state information, and displays a marker indicating the detected location over the map. Whenever an event occurs, an additional marker is displayed over the map and the history of the past events is recorded on the map.