A transmission device for converting a torque comprising: a rack having a plurality of rack tooth profiles; a plurality of pin gears provided separated from each other in a lengthwise direction of the rack, each pin gear having a plurality of power transmission pins relatively rotating along the plurality of rack tooth profiles for power transmission; and an input gear arranged between the pin gears and connecting the plurality of pin gears to be capable of rotating to allow the plurality of pin gears to rotate at the same speed, characterized in that each of the plurality of pin gears comprises: a body for rotatably supporting the plurality of power transmission pins; and a rotation support bearing unit coupled to a center area of the body and supporting a rotational motion of the body, wherein the rotation support bearing unit comprises a center portion rotation shaft provided at a rotation center portion of the body and forming a center of rotation with respect to the body and a center of revolution with respect to the plurality of power transmission pins, wherein a plurality of pin support bearings is arranged at an equiangular interval along a circumferential direction of the body as many as the number of the plurality of power transmission pins and supporting rotational motions of the plurality of power transmission pins, wherein the center portion rotation shaft is coupled to the body by a plurality of coupling members, wherein the input gear comprises an input gear main body where a plurality of input tooth profiles are formed on an outer surface along a circumferential direction thereof to correspond to the plurality of power transmission pins of the plurality of pin gears and interact with the plurality of power transmission pins. a rack having a plurality of rack tooth profiles; a plurality of pin gears provided separated from each other in a lengthwise direction of the rack, each pin gear having a plurality of power transmission pins relatively rotating along the plurality of rack tooth profiles for power transmission; and an input gear arranged between the pin gears and connecting the plurality of pin gears to be capable of rotating to allow the plurality of pin gears to rotate at the same speed, characterized in that each of the plurality of pin gears comprises: a body for rotatably supporting the plurality of power transmission pins; and a rotation support bearing unit coupled to a center area of the body and supporting a rotational motion of the body, a body for rotatably supporting the plurality of power transmission pins; and a rotation support bearing unit coupled to a center area of the body and supporting a rotational motion of the body, wherein the rotation support bearing unit comprises a center portion rotation shaft provided at a rotation center portion of the body and forming a center of rotation with respect to the body and a center of revolution with respect to the plurality of power transmission pins, wherein a plurality of pin support bearings is arranged at an equiangular interval along a circumferential direction of the body as many as the number of the plurality of power transmission pins and supporting rotational motions of the plurality of power transmission pins, wherein the center portion rotation shaft is coupled to the body by a plurality of coupling members, wherein the input gear comprises an input gear main body where a plurality of input tooth profiles are formed on an outer surface along a circumferential direction thereof to correspond to the plurality of power transmission pins of the plurality of pin gears and interact with the plurality of power transmission pins.