ON-VEHICLE INTRUSION DETECTOR

A vehicle-mounted intrusion detection apparatus for detecting an intrusion into a vehicle based on a wave transmitted inside the vehicle and reflected from an object located inside the vehicle, wherein the vehicle-mounted intrusion detection apparatus is configured so as not to recognize the reflected wave as indicating an intrusion if an output level of the reflected wave, after reaching or exceeding a first output level, has reached or exceeded a second output level higher than the first output level within a predetermined time.