A denture-fixing attachment comprising: a fixture able to be implanted into an implant groove formed in an alveolar bone, said fixture including a fixing groove; a rotation guide member comprising a lower portion extending downward to be inserted into the fixture groove of the fixture such that the rotation guide member is coupled with the fixture, said lower portion being provided at an outer portion thereof with a thread; said rotation guide member also comprising a lateral surface positioned above the lower portion; said rotation guide member also comprising an upper protrusion protruding in a shape of a ball at an upper end of the rotation guide member; a ball joint angle restriction cover comprising an outer lateral wall defining an inner space, said lateral wall suitable for being assembled to the lateral surface of the rotation guide member so that said lateral surface is received inside the inner space, said cover having a through hole vertically formed at an upper portion thereof; and a ball joint having a lower portion in a shape of a bow, adapted to be placed on the upper protrusion of the rotation guide member in the inner space of the ball joint angle restriction cover, so as to be freely adjustable in angle and position, wherein the ball joint has a shape of a dumbbell and also comprises: an intermediate portion provided above the lower portion, said intermediate portion having a diameter smaller than a diameter of the lower portion, and having a shape of a cylinder; and an upper portion fixed to an upper end of the intermediate portion, said upper portion having a shape of a ball of a diameter greater than the diameter of the intermediate portion and smaller than the diameter of the lower portion, said intermediate portion and upper portion protruding upward through the through hole of the ball-joint restriction cover, said through hole thereby forming an angle restriction to the ball joint. a fixture able to be implanted into an implant groove formed in an alveolar bone, said fixture including a fixing groove; a rotation guide member comprising a lower portion extending downward to be inserted into the fixture groove of the fixture such that the rotation guide member is coupled with the fixture, said lower portion being provided at an outer portion thereof with a thread; said rotation guide member also comprising a lateral surface positioned above the lower portion; said rotation guide member also comprising an upper protrusion protruding in a shape of a ball at an upper end of the rotation guide member; a ball joint angle restriction cover comprising an outer lateral wall defining an inner space, said lateral wall suitable for being assembled to the lateral surface of the rotation guide member so that said lateral surface is received inside the inner space, said cover having a through hole vertically formed at an upper portion thereof; and a ball joint having a lower portion in a shape of a bow, adapted to be placed on the upper protrusion of the rotation guide member in the inner space of the ball joint angle restriction cover, so as to be freely adjustable in angle and position, wherein the ball joint has a shape of a dumbbell and also comprises: an intermediate portion provided above the lower portion, said intermediate portion having a diameter smaller than a diameter of the lower portion, and having a shape of a cylinder; and an upper portion fixed to an upper end of the intermediate portion, said upper portion having a shape of a ball of a diameter greater than the diameter of the intermediate portion and smaller than the diameter of the lower portion, said intermediate portion and upper portion protruding upward through the through hole of the ball-joint restriction cover, said through hole thereby forming an angle restriction to the ball joint.