A module bearing comprising: a module outer wheel supported by and in contact with a side wall of a gear to guide rotational or linear motion of the gear; a bearing rotating body rotatably disposed radially inward of the module outer wheel; and a part-assembly type module inner wheel disposed radially inward of the module outer wheel with the bearing rotating body interposed therebetween and connected to the bearing rotating body, wherein a plurality of separate parts are manufactured and assembled into the part-assembly type module inner wheel to apply a preload to the bearing rotating body, wherein the part-assembly type module inner wheel comprises: a first inner wheel part having a first support wall supported by one end portion of the bearing rotating body; and a second inner wheel part having a second support wall supported by the other end portion of the bearing rotating body at an opposite side of the bearing rotating body, wherein the first inner wheel part comprises: a first inner wheel insertion portion inserted into the bearing rotating body; and a first inner wheel flange portion connected to the first inner wheel insertion portion, having a diameter greater than a diameter of the first inner wheel insertion portion, and forming the first support wall between the first inner wheel insertion portion and the first inner wheel flange portion, characterised in that the second inner wheel part comprises: a second inner wheel insertion portion inserted into the bearing rotating body and surface-contacting an end portion of the first inner wheel insertion portion inside the bearing rotating body; and a second inner wheel flange portion connected to the second inner wheel insertion portion, having a diameter greater than a diameter of the second inner wheel insertion portion, and forming the second support wall between the second inner wheel insertion portion and the second inner wheel flange portion. a module outer wheel supported by and in contact with a side wall of a gear to guide rotational or linear motion of the gear; a bearing rotating body rotatably disposed radially inward of the module outer wheel; and a part-assembly type module inner wheel disposed radially inward of the module outer wheel with the bearing rotating body interposed therebetween and connected to the bearing rotating body, wherein a plurality of separate parts are manufactured and assembled into the part-assembly type module inner wheel to apply a preload to the bearing rotating body, wherein the part-assembly type module inner wheel comprises: a first inner wheel part having a first support wall supported by one end portion of the bearing rotating body; and a second inner wheel part having a second support wall supported by the other end portion of the bearing rotating body at an opposite side of the bearing rotating body, wherein the first inner wheel part comprises: a first inner wheel insertion portion inserted into the bearing rotating body; and a first inner wheel flange portion connected to the first inner wheel insertion portion, having a diameter greater than a diameter of the first inner wheel insertion portion, and forming the first support wall between the first inner wheel insertion portion and the first inner wheel flange portion, a first inner wheel part having a first support wall supported by one end portion of the bearing rotating body; and a second inner wheel part having a second support wall supported by the other end portion of the bearing rotating body at an opposite side of the bearing rotating body, wherein the first inner wheel part comprises: a first inner wheel insertion portion inserted into the bearing rotating body; and a first inner wheel flange portion connected to the first inner wheel insertion portion, having a diameter greater than a diameter of the first inner wheel insertion portion, and forming the first support wall between the first inner wheel insertion portion and the first inner wheel flange portion, a first inner wheel insertion portion inserted into the bearing rotating body; and a first inner wheel flange portion connected to the first inner wheel insertion portion, having a diameter greater than a diameter of the first inner wheel insertion portion, and forming the first support wall between the first inner wheel insertion portion and the first inner wheel flange portion, characterised in that the second inner wheel part comprises: a second inner wheel insertion portion inserted into the bearing rotating body and surface-contacting an end portion of the first inner wheel insertion portion inside the bearing rotating body; and a second inner wheel flange portion connected to the second inner wheel insertion portion, having a diameter greater than a diameter of the second inner wheel insertion portion, and forming the second support wall between the second inner wheel insertion portion and the second inner wheel flange portion. a second inner wheel insertion portion inserted into the bearing rotating body and surface-contacting an end portion of the first inner wheel insertion portion inside the bearing rotating body; and a second inner wheel flange portion connected to the second inner wheel insertion portion, having a diameter greater than a diameter of the second inner wheel insertion portion, and forming the second support wall between the second inner wheel insertion portion and the second inner wheel flange portion.