A driving support ECU includes: a lateral width acquisition unit that acquires from an image a dimension of an object in a lateral direction with respect to an imaging direction of an imaging means as a lateral width; a determination unit that compares the current lateral width with a past lateral width to determine whether the current width is smaller than the past lateral width; and a correction unit that, when the current lateral width is smaller than the past lateral width, corrects right and left end positions of the lateral width based on whichever is smaller, the deviation amount of the right end position of the object or the deviation amount of the left and position of the object.