There is provided an implant having a slack prevention function by an eccentric fitting structure. An engaging shaft (53), which is decentered with a screw shaft (52), is provided at the end of an abutment screw (5), and is engaged with an engaging hole (45) provided in the bottom of a screw hole (44), into which an abutment screw (5) is screwed, and thus, the screw shaft (52) is inclined to and eccentric from the screw hole (44). Thereby, the screw shaft (52) comes to be strongly pressed partially in a circumferential direction toward the screw hole (44), so that internal stress in the horizontal direction is accumulated on the screw shaft (52). The screw (5) is threaded with maintaining prevailing torque caused by the internal stress, which enables the screw (5) to be fastened to the right position.
