Abstract: To provide a fastening tool that can solve problems that are raised upon locking the opening portion of clothing, baggage or the like, and can also positively lock the portion to be locked at a desired position without the necessity of any processing jobs, such as caulking, sewing and the like, so as to be freely detachably locked. The fastening tool is provided with at least a pair of fastening members a and b which have detachably attaching portions that are freely detachably attached to each other, and each of the fastening members a and b has a substrate with a piercing needle formed on one of the surfaces, a bottom plate that is penetrated by the piercing needle, a pierce catch made of a cap-shaped member to cover the tip of the penetrated piercing needle, and detachably attaching portions that are freely detachably engaged with each other.