1. An object detection apparatus, comprising: a first direction contour component extraction unit configured to extract, from an image, a contour component in a first direction of the image; a second direction continuity detection unit configured to detect, in a second direction perpendicular to the first direction, a continuity of the contour component extracted by the first direction contour component extraction unit; an object area detection unit configured to detect a first end point and a second end point of each image area that has been determined to have continuity in the second direction by the second direction continuity detection unit, the first end point being an end point in the second direction and the second end point being another end point in the second direction, and to detect a contour of an object in the image by estimating a contour line of the object in the first direction based on the detected first end point and the detected second end point; and a central axis detection unit configured to detect an axis of symmetry of a substantially line-symmetric object included in the image, the axis of symmetry of the object being parallel to the first direction, wherein the second direction continuity detection unit detects the continuity of the contour component in the second direction based on the axis of symmetry detected by the central axis detection unit.