VEHICLE ANTI-THEFT DEVICE, VEHICLE ANTI-THEFT METHOD, AND COMPUTER PROGRAM

This vehicle anti-theft device comprises: a wireless receiver that is installed in a vehicle and receives information including the ID of a portable device transmitted wirelessly from the portable device; a first registration processing unit that registers a first ID received by the wireless receiver, using a predefined procedure, as the ID of the portable device belonging to an owner group; a second registration processing unit that, when a second ID is received by the wireless receiver together with the ID registered by the first registration processing unit, registers the second ID as the ID of the portable device belonging to an affiliate group; and a theft determination processing unit that, on detecting movement of the vehicle without having received the ID registered by the first registration processing unit or the ID registered by the second registration processing unit at that time, determines that the vehicle is in a stolen state.