1. A position and orientation measurement apparatus comprising: a storage unit configured to store a three-dimensional model of a target object; a two-dimensional image obtaining unit configured to obtain a two-dimensional image of the target object; an extraction unit configured to extract an occluded region in which illumination irradiated onto the target object is occluded in the two-dimensional image; a projection unit configured to project a geometric feature that constitutes the three-dimensional model onto the two-dimensional image based on approximate values of position and orientation of the target object; an association unit configured to associate the geometric feature with an image feature in the two-dimensional image; a determination unit configured to determine whether the associated image feature in the two-dimensional image is on a contour of the occluded region; and a position and orientation measurement unit configured to measure the position and orientation of the target object based on a distance on the two-dimensional image between the projected geometric feature and the associated image feature in the two-dimensional image, in accordance with a determination result by the determination unit.