A feeding device includes a paper feed tray, a detector on an image forming apparatus main body, a control member rotatably supported by the paper feed tray, and spacers. The detector includes movable pieces and contact points corresponding to the movable piece, and switches each contact point by the position of the corresponding movable piece. The control member includes a control surface formed on its outer circumferential surface with projecting and recessed portions. The projecting and recessed portions are disposed in a pattern corresponding to rotation angles in an area of the control surface facing the movable pieces. Controlling the positions of the movable pieces according to the pattern encodes paper size. Each movable piece is lined in the circumferential direction facing the control surface. The outer circumferential surface of the projecting portions is formed in a cylindrical surface shape centering around the rotational axis of the control member.