An electric power steering apparatus comprising: an input shaft to which steering force from a steering wheel is applied; an output shaft to which auxiliary power generated by an electric motor is applied; a torsion bar provided in a radially inner side of the input shaft and the output shaft and coaxially coupling the input shaft and the output shaft to each other; and a torque detection sleeve, wherein one of the input shaft and the output shaft comprises a cylindrical portion provided at an end portion of the one of the input shaft and the output shaft that is coupled to the other of the input shaft and the output shaft, wherein the cylindrical portion comprises a female stopper provided on an inner peripheral surface of the cylindrical portion, the female stopper comprising a plurality of female teeth and a plurality of female grooves, and the plurality of female teeth and the plurality of female grooves extending in an axial direction and being alternately arranged in a circumferential direction, wherein the other of the input shaft and the output shaft comprises a male stopper provided on an outer peripheral surface of an end portion of the other of the input shaft and the output shaft that is coupled to the one of the input shaft and the output shaft, and a torque detection concave-convex section provided on an outer peripheral surface of another portion the other of the input shaft and the output shaft that is adjacent to the male stopper with respect to the axial direction, wherein the male stopper comprises a plurality of male teeth and a plurality of male grooves, the plurality of male teeth and the plurality of male grooves extending in the axial direction and being alternately arranged in the circumferential direction, and the male stopper being engaged with the female stopper in a concave-convex engaging manner so as to be relatively rotatable in a given angle range, wherein the torque detection concave-convex section comprises a plurality of detection grooves, the plurality of detection grooves extending in the axial direction and being arranged at equal intervals in the circumferential direction, wherein the torque detection sleeve is arranged on a radially outer side of the torque detection concave-convex section, the torque detection sleeve comprising a base end portion fitted and fixed on the cylindrical portion, characterized in that a diameter (d) of a groove bottom circle of the male stopper is smaller than a diameter of a groove bottom circle of the torque detection concave-convex section. an input shaft to which steering force from a steering wheel is applied; an output shaft to which auxiliary power generated by an electric motor is applied; a torsion bar provided in a radially inner side of the input shaft and the output shaft and coaxially coupling the input shaft and the output shaft to each other; and a torque detection sleeve, wherein one of the input shaft and the output shaft comprises a cylindrical portion provided at an end portion of the one of the input shaft and the output shaft that is coupled to the other of the input shaft and the output shaft, wherein the cylindrical portion comprises a female stopper provided on an inner peripheral surface of the cylindrical portion, the female stopper comprising a plurality of female teeth and a plurality of female grooves, and the plurality of female teeth and the plurality of female grooves extending in an axial direction and being alternately arranged in a circumferential direction, wherein the other of the input shaft and the output shaft comprises a male stopper provided on an outer peripheral surface of an end portion of the other of the input shaft and the output shaft that is coupled to the one of the input shaft and the output shaft, and a torque detection concave-convex section provided on an outer peripheral surface of another portion the other of the input shaft and the output shaft that is adjacent to the male stopper with respect to the axial direction, wherein the male stopper comprises a plurality of male teeth and a plurality of male grooves, the plurality of male teeth and the plurality of male grooves extending in the axial direction and being alternately arranged in the circumferential direction, and the male stopper being engaged with the female stopper in a concave-convex engaging manner so as to be relatively rotatable in a given angle range, wherein the torque detection concave-convex section comprises a plurality of detection grooves, the plurality of detection grooves extending in the axial direction and being arranged at equal intervals in the circumferential direction, wherein the torque detection sleeve is arranged on a radially outer side of the torque detection concave-convex section, the torque detection sleeve comprising a base end portion fitted and fixed on the cylindrical portion, characterized in that a diameter (d) of a groove bottom circle of the male stopper is smaller than a diameter of a groove bottom circle of the torque detection concave-convex section.