An electric power steering apparatus comprising: an input shaft to which steering force is applied from a steering wheel; an output shaft to which assisting force generated by an electric motor is applied; a torsion bar provided radially inside the input shaft and the output shaft in a state in which the input shaft and the output shaft are coaxially connected to each other; and a torque detection sleeve, wherein one of the input shaft and the output shaft comprises a cylindrical portion, the cylindrical portion being provided at an end section of the one of the input shaft and the output shaft that is connected to the other of the input shaft and the output shaft, wherein the cylindrical portion comprises a female stopper portion having a concave-convex shape along a circumferential direction and provided on an inner peripheral surface of the cylindrical portion, a circumferential groove provided along the circumferential direction of the cylindrical portion, wherein the other of the input shaft and the output shaft comprises a male stopper portion having a concave-convex shape along the circumferential direction and provided on an outer peripheral surface of an end section of the other of the input shaft and the output shaft that is connected to the one of the input shaft and the output shaft, the male stopper portion being in concave-convex engagement with the female stopper portion so as to be relatively rotatable in a given angular range, and a torque detection concave-convex portion having a concave-convex shape along the circumferential direction and provided on a portion of an outer peripheral surface of the other of the input shaft and the output shaft that is adjacent to the male stopper portion in the axial direction, wherein the torque detection sleeve is disposed radially outside the torque detection concave-convex portion, wherein a base end portion of the torque detection sleeve is securely fitted on the cylindrical portion in a state in which an edge portion of the base end portion is clinched to the circumferential groove, characterized in that the circumferential groove is provided on a portion of the outer peripheral surface of the cylindrical portion radially overlapping a stopper engagement region in which the female stopper portion and the male stopper portion are engaged with each other, an auxiliary circumferential groove is provided along the circumferential direction on the portion on the outer peripheral surface of the cylindrical portion radially overlapping the stopper engagement region and at a location between the circumferential groove and a distal end of the cylindrical portion, and wherein a portion of the base end portion of the torque detection sleeve is clinched to the auxiliary circumferential groove. an input shaft to which steering force is applied from a steering wheel; an output shaft to which assisting force generated by an electric motor is applied; a torsion bar provided radially inside the input shaft and the output shaft in a state in which the input shaft and the output shaft are coaxially connected to each other; and a torque detection sleeve, wherein one of the input shaft and the output shaft comprises a cylindrical portion, the cylindrical portion being provided at an end section of the one of the input shaft and the output shaft that is connected to the other of the input shaft and the output shaft, wherein the cylindrical portion comprises a female stopper portion having a concave-convex shape along a circumferential direction and provided on an inner peripheral surface of the cylindrical portion, a circumferential groove provided along the circumferential direction of the cylindrical portion, wherein the other of the input shaft and the output shaft comprises a male stopper portion having a concave-convex shape along the circumferential direction and provided on an outer peripheral surface of an end section of the other of the input shaft and the output shaft that is connected to the one of the input shaft and the output shaft, the male stopper portion being in concave-convex engagement with the female stopper portion so as to be relatively rotatable in a given angular range, and a torque detection concave-convex portion having a concave-convex shape along the circumferential direction and provided on a portion of an outer peripheral surface of the other of the input shaft and the output shaft that is adjacent to the male stopper portion in the axial direction, wherein the torque detection sleeve is disposed radially outside the torque detection concave-convex portion, wherein a base end portion of the torque detection sleeve is securely fitted on the cylindrical portion in a state in which an edge portion of the base end portion is clinched to the circumferential groove, the circumferential groove is provided on a portion of the outer peripheral surface of the cylindrical portion radially overlapping a stopper engagement region in which the female stopper portion and the male stopper portion are engaged with each other, an auxiliary circumferential groove is provided along the circumferential direction on the portion on the outer peripheral surface of the cylindrical portion radially overlapping the stopper engagement region and at a location between the circumferential groove and a distal end of the cylindrical portion, and wherein a portion of the base end portion of the torque detection sleeve is clinched to the auxiliary circumferential groove.