Provided is straightening tool for deformed nails which, even for badly deformed nails with heavy deformation or curvature, or for deformed nails in which the lateral edges of the nail are shaped irregularly, allows easy insertion up to near the root of the nail without causing the patient pain while mounted, and thereby achieves a greater straightening effect and prevents recurrence of deformed nails. This straightening tool is characterized by including a band-shape central region which is to be brought into contact against the top surface of the nail, and an insertion edge region which extends continuously from at least one end of the band-shape central region and which is for insertion between the side lines and the side walls； and is characterized in that, defining the direction towards the nail root as up and the direction towards the nail tip as down when mounting the straightening tool on the nail, a screw blade portion having a specific shape and dimensions is formed in a position that includes the upper end portion of the insertion edge region, and a hook portion for holding the side line portion of the nail or the lateral edge of the nail tip is formed downwards of the screw blade portion of the insertion edge region.
