Abstract: A device for straightening one edge DA of the four side edges AB, BC, CD and DA of a flexible sheet such as a crumpled bed sheet disclosed. One corner A of the sheet and a portion of the edge AB are held by a pair of laterally spaced apart, left and right holders mounted on a movable member so that the sheet is displaced on an elongated plate along the longitudinal direction thereof by the movement of the movable member. One or more laterally extending endless conveyers belts are provided on the plate to laterally move the sheet on the plate. A detector is provided to determine the direction of the movement of each of the conveyors, so that the edge DA is made in parallel with the longitudinal direction of the plate.