Abstract: A self-contained hand tool for driving fence posts into the earth and operable by an automobile battery, or the like. The tool comprises a sleeve member for receiving one end of the post therein, reciprocal hammer means disposed within the sleeve and intermittently engagable with the post, power means, cam means, drive means operably connected between the power means and the cam means for rotation thereof, extension strap means carried by the hammer means and engagable by the cam means during rotation thereof for moving the hammer means in one direction, and yieldable means connected with the hammer means for returning the hammer means to the normal position thereof against the action of the cam and strap means for providing said reciprocal movement for the hammer means.