In order to detect an object by discriminating the object in accordance with the state of the object, a detection device comprises: a detection unit configured to detect a plurality of portions of an object contained in a frame image of a moving image; an intrusion determination unit configured to determine that the object has intruded into a preset area of the frame image; and a determination unit configured to determine whether to notify a determination result of the intrusion determination unit, in accordance with whether portions detected by the detection unit include a predetermined portion.