An image forming apparatus includes an intermediate transfer belt that moves while keeping contact with a photosensitive element at a transfer position, a control pattern forming unit that forms a control pattern on the intermediate transfer belt, a control pattern detecting unit that detects the control pattern; a deformation preventing unit arranged on a rear side of the moving member at a position facing the control pattern detecting unit; and tension applying members that applies tension to the intermediate transfer belt to tautly support the intermediate transfer belt. The deformation preventing unit and one of the tension applying members being a bias impressing unit that impresses a bias are arranged in close proximity to each other, and a surface of the deformation preventing unit is formed with an insulating material.