The conventional image surveillance technologies relevant to the present invention had the potential of failing in detect ion due to the intrusion duration time being set too long and thereby allowing an intruder to pass a warning line before the preset intrusion duration had elapsed. The intrusion detection device according to the present invention is provided with: a detect ion means that detects, in an image, an intrusion position in a specific region by an object that has intruded into the specific region; and a control means that associates the intrusion position with a prescribed time period, wherein the detection means outputs an alert when the object, in the image, has stayed in the specific region for the prescribed time period or longer.