A seatbelt retractor comprising: a take-up drum configured to take up and store a webbing; a housing having a pair of side wall portions (21, 22) which face each other, the pair of side wall portions (21, 22) consisting of a one-side wall portion and the other-side wall portion each of which having a through hole (28, 38) configured to allow insertion of the take-up-drum and rotatably hold the take-up drum; and a locking means (28A, 29) arranged between the take-up drum and a through hole at the one-side wall portion, the locking means (28A, 29) normally allowing the take-up drum to rotate, and getting activated when needed so as to stop the take-up drum from rotating in a webbing-pull-out direction, wherein the take-up drum comprises: a webbing take-up portion; and a pair of flange portions (132, 133) provided at axis directional both ends of the webbing-take-up portion, one of which positioned at the one-side wall portion of the housing being an engagement-side flange portion, wherein the locking means (28A, 29) comprises: engagement teeth formed on inner periphery of the through hole at the one-side wall portion; and a pawl mounted on the engagement-side flange portion that faces the engagement teeth, the pawl normally being set at a disengagement position so as to be disengaged from the engagement teeth and brought to an engagement position so as to get engaged with the engagement teeth when needed, wherein the engagement-side flange portion comprises a projecting portion formed so as to project radially outward from a peripheral edge thereof, opposing to the pawl at the engagement position, and wherein, in a state where center axis of the through hole at the one side wall portion and rotation axis of the take-up drum align, an axially outer surface of the projecting portion faces the engagement teeth and the projecting portion projects radially outward over an inner peripheral diameter defined with tip ends of the engagement teeth, characterized in that outer peripheral diameter of the engagement-side flange portion is set smaller than the inner peripheral diameter defined with tip ends of the engagement teeth and maximum outer peripheral dimension formed by the projecting portion and the engagement-side flange portion is set larger than the inner peripheral diameter defined with tip ends of the engagement teeth. a take-up drum configured to take up and store a webbing; a housing having a pair of side wall portions (21, 22) which face each other, the pair of side wall portions (21, 22) consisting of a one-side wall portion and the other-side wall portion each of which having a through hole (28, 38) configured to allow insertion of the take-up-drum and rotatably hold the take-up drum; and a locking means (28A, 29) arranged between the take-up drum and a through hole at the one-side wall portion, the locking means (28A, 29) normally allowing the take-up drum to rotate, and getting activated when needed so as to stop the take-up drum from rotating in a webbing-pull-out direction, wherein the take-up drum comprises: a webbing take-up portion; and a pair of flange portions (132, 133) provided at axis directional both ends of the webbing-take-up portion, one of which positioned at the one-side wall portion of the housing being an engagement-side flange portion, wherein the locking means (28A, 29) comprises: engagement teeth formed on inner periphery of the through hole at the one-side wall portion; and a pawl mounted on the engagement-side flange portion that faces the engagement teeth, the pawl normally being set at a disengagement position so as to be disengaged from the engagement teeth and brought to an engagement position so as to get engaged with the engagement teeth when needed, wherein the engagement-side flange portion comprises a projecting portion formed so as to project radially outward from a peripheral edge thereof, opposing to the pawl at the engagement position, and wherein, in a state where center axis of the through hole at the one side wall portion and rotation axis of the take-up drum align, an axially outer surface of the projecting portion faces the engagement teeth and the projecting portion projects radially outward over an inner peripheral diameter defined with tip ends of the engagement teeth, characterized in that outer peripheral diameter of the engagement-side flange portion is set smaller than the inner peripheral diameter defined with tip ends of the engagement teeth and maximum outer peripheral dimension formed by the projecting portion and the engagement-side flange portion is set larger than the inner peripheral diameter defined with tip ends of the engagement teeth.