1. An object detection apparatus comprising: an image obtaining unit configured to sequentially obtain a plurality of frame images; a detection unit configured to calculate a detection likelihood from each of the plurality of frame images, and to detect a target object from each of the frame images on the basis of the detection likelihood; and a tracking unit configured to calculate a tracking likelihood of the target object from each of the plurality of frame images, and to track the target object over the plurality of frame images on the basis of the tracking likelihood, wherein the detection unit detects the target object from the frame images obtained by the image obtaining unit on the basis of the tracking likelihood of the target object that is calculated by the tracking unit from the frame images, and the detection likelihood of the target object that is calculated by the detection unit from the frame images.