A orthodontic medical device comprising: a shaft portion with a hollow shape, the shaft portion being configured to be inserted into a cortical bone or the shaft portion being configured to penetrate through the cortical bone and to be inserted to a position reaching a cancellous bone at an inner side of the cortical bone; and an exposed portion that includes a portion (70A2) extending to a radial direction outer side from one end portion of an axial direction of the shaft portion, the exposed portion being configured to be exposed at a surface of the cortical bone, and wherein the one end portion of the shaft portion is closed off by a portion (70A1) of the exposed portion, and at least a portion of a surface, at the opposite side of the exposed portion from the side thereof at which the shaft portion, is configured to be exposed from an epithelium that covers the cortical bone, wherein one or more slits along the axial direction are provided at the shaft portion, wherein the slits are formed over substantially a whole length in the axial direction of the shaft portion, one length direction end of the slit being formed with an opening at a distal end of the shaft portion at an opposite side of the exposed portion, and an outer diameter of the shaft portion being configured to deform in directions of expansion and contraction, wherein the shaft portion with the hollow shape is configured to enable the cells with the bone-forming function to migrate through the shaft portion with the hollow shape, the slits are configured to enable the cells with a bone-forming function to migrate from inside the bone through the slit, and new bone to be formed by the cells at an inner face side of the shaft portion, promoting bonding to the bone; characterized in that the length in the axial direction of the shaft portion is set to be around 1.5 mm or to be around 2 0 mm a shaft portion with a hollow shape, the shaft portion being configured to be inserted into a cortical bone or the shaft portion being configured to penetrate through the cortical bone and to be inserted to a position reaching a cancellous bone at an inner side of the cortical bone; and an exposed portion that includes a portion (70A2) extending to a radial direction outer side from one end portion of an axial direction of the shaft portion, the exposed portion being configured to be exposed at a surface of the cortical bone, and wherein the one end portion of the shaft portion is closed off by a portion (70A1) of the exposed portion, and at least a portion of a surface, at the opposite side of the exposed portion from the side thereof at which the shaft portion, is configured to be exposed from an epithelium that covers the cortical bone, wherein one or more slits along the axial direction are provided at the shaft portion, wherein the slits are formed over substantially a whole length in the axial direction of the shaft portion, one length direction end of the slit being formed with an opening at a distal end of the shaft portion at an opposite side of the exposed portion, and an outer diameter of the shaft portion being configured to deform in directions of expansion and contraction, wherein the shaft portion with the hollow shape is configured to enable the cells with the bone-forming function to migrate through the shaft portion with the hollow shape, the slits are configured to enable the cells with a bone-forming function to migrate from inside the bone through the slit, and new bone to be formed by the cells at an inner face side of the shaft portion, promoting bonding to the bone; characterized in that the length in the axial direction of the shaft portion is set to be around 1.5 mm or to be around 2 0 mm