To provide a crime prevention system which holds photographic image data until a monitor unit stops operating and transmits an alarm and the photographic image data to a security management organization or security agency even if no electric power is sent to the monitor unit or when the monitor unit gets out of order or is to be broken.

A plurality of monitor units 101 are connected by a network and image data photographed by an image photographing means are stored in a storage means; and then one of the monitor units 101 holds the data as a backup and this normal monitor unit generates an alarm and transmits the image data to an information terminal with a predetermined address.