ALERT DEVICE, ALERT METHOD, AND ALERT PROGRAM

To issue an appropriate warning based on detection of an object even under the circumstances where it is difficult to determine the outside environment of a movable body, a warning device (10) according to the present invention includes an image acquisition means (11) for acquiring a plurality of images respectively based on a plurality of filter characteristics, a detection means (12) for performing detection of a specified object on each of the plurality of acquired images, and a warning means (13) for issuing a specific warning when the object is detected from at least any one of the plurality of acquired images, wherein the warning means (13) issues a higher level of warning when the object is detected from all of the plurality of images than when the object is detected from some of the plurality of images.