The misalignment quantity calculating apparatus determines whether a first object detected by a beam sensor is identical to a second object detected by an image sensor. Upon determining that the first object is identical to the second object, the misalignment quantity calculating apparatus calculates, as a misalignment quantity of the beam sensor, an angle between a first line segment and a second line segment; the first line segment connects a predetermined reference point of the misalignment quantity calculating apparatus and a first feature point of the first object, and the second line segment connects the predetermined reference point and a second feature point of the second object.