A sufficient gripping force is exerted on a suture thread through an easy process. Provided is a ligation thread fastening tool including: a gripper that has a pair of crimp pieces opposed to each other with a space therebetween and whose inner faces opposed to each other are to be crimped together and that has, between the inner faces, a groove into which a suture thread can be inserted from a first side of the crimp pieces toward a second side thereof; and an accommodation portion that is provided in the gripper from the inner face outward of the groove so as to communicate with the groove and that accommodate an end portion of the suture thread inserted thereinto from the first side through the groove.