Abstract: A board straightening device which embodies levers to expand a concentric piping arrangement, one end of which is fixed on a joist, rafter stud, or other board supporting member, and the other end is placed against a crooked board, such as decking or siding, which is being nailed across the board supporting member. The device includes a cleated foot for gripping the board supporting member, the foot being attached to a pipe member which fits concentrically with another pipe member to which is attached the head or pushing end of the device. A lever arrangement connecting the two pipe members causes them to relatively displace when a lever handle is pushed toward the device. A head attachment, configured to the shape of the board to minimize damage, pushes against and straightens the crooked board for nailing. Limiting and adjusting means for displacement and leverage may be used.