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.
