1. An object detection apparatus that detects a target object from image data, the apparatus comprising: an image obtaining unit adapted to obtain image data by sequentially capturing an image in a predetermined direction from a predetermined viewpoint; a feature extraction unit adapted to extract a feature amount for each of partial regions that constitute the image data obtained by the image obtaining unit; a storage unit adapted to store, as a background feature amount for each of the partial regions, a feature amount extracted in advance by the feature extraction unit from background image data that has been obtained by the image obtaining unit and does not include the target object; a first object region determination unit adapted to determine, for each of the partial regions, whether or not the partial region is an object region including the target object by comparing a current feature amount extracted from the partial region by the feature extraction unit with the background feature amount; a statistic calculation unit adapted to calculate, for each of the partial regions, a statistic of determination within a period by the first object region determination unit, based on determination results by the first object region determination unit within the period; a parameter deciding unit adapted to decide a parameter for each of the partial regions based on a statistic of incorrect determination calculated by the statistic calculation unit within a parameter setting period in which the partial region does not include the target object but is incorrectly determined as the object region by the first object region determination unit; and a second object region determination unit adapted to determine, for each of the partial regions determined as the object region by the first object region determination unit within a detection period in which the object would be detected, whether the partial region is the object region or a disturbance, based on the parameter decided by the parameter deciding unit and the statistic of determination within the detection period calculated by the statistic calculation unit.