Provided is a corrective device for ingrown toenails and incurvated toenails. The corrective device includes a central member made of a shape-memory alloy; and prefabricated toenail side-engaging parts, each being attached to both ends of the central member. The corrective device of the present invention has advantages such as provision of strong corrective force over the entire toenail, convenient use, suitability for long-term use, straight growth of a toenail that will grow after a surgical treatment of the ingrown toenail, and straightening of a curved toenail.