A steering device comprising: an inner column; a hollow cylindrical single piece outer column formed of an aluminium alloy or a magnesium alloy fitted, axially relatively movably, over the inner column; a steering shaft which is axially rotatably supported by the outer column and which can be attached with a steering wheel at a portion thereof toward a vehicle rear side; a steering lock device which is attached to the outer column and which causes a lock pin operated by operation of an ignition key to engage the steering shaft so as to lock the steering shaft not to allow the steering shaft to rotate; a slit formed to extend over a predetermined length along an axial direction of the outer column; a clamp device which can axially relatively immovably clamp the inner column by contracting a diameter of the outer column; a through hole formed in the outer column such that the through hole is circumferentially spaced, about an axis of the outer column, from the slit; and a flange section (43, 44) which is formed integrally with an outer peripheral surface portion between the slit and the through hole on the outer column, which projects radially outwardly from the outer peripheral surface portion and to which a housing to accommodate the steering lock device is attached, wherein the flange section (43, 44) includes a rib (432, 433, 442, 443) formed to connect the flange section (43, 44) and the outer peripheral surface of the outer column so as to reinforce the flange section (43, 44), wherein the rib (432, 433, 442, 443) extends to near a closed end of the slit so as to reinforce a neighborhood portion of the closed end of the slit, and wherein the outer column includes a thin part formed, near the closed end of the slit, on the outer peripheral surface thereof so as to allow the diameter thereof to be contracted easily, wherein clearance is formed between the through hole and an outer peripheral surface of the lock pin, so that a bending moment applied to the lock pin is borne only by the flange section (43, 44) when the lock pin is engaged with the steering shaft. an inner column; a hollow cylindrical single piece outer column formed of an aluminium alloy or a magnesium alloy fitted, axially relatively movably, over the inner column; a steering shaft which is axially rotatably supported by the outer column and which can be attached with a steering wheel at a portion thereof toward a vehicle rear side; a steering lock device which is attached to the outer column and which causes a lock pin operated by operation of an ignition key to engage the steering shaft so as to lock the steering shaft not to allow the steering shaft to rotate; a slit formed to extend over a predetermined length along an axial direction of the outer column; a clamp device which can axially relatively immovably clamp the inner column by contracting a diameter of the outer column; a through hole formed in the outer column such that the through hole is circumferentially spaced, about an axis of the outer column, from the slit; and a flange section (43, 44) which is formed integrally with an outer peripheral surface portion between the slit and the through hole on the outer column, which projects radially outwardly from the outer peripheral surface portion and to which a housing to accommodate the steering lock device is attached, wherein the flange section (43, 44) includes a rib (432, 433, 442, 443) formed to connect the flange section (43, 44) and the outer peripheral surface of the outer column so as to reinforce the flange section (43, 44), wherein the rib (432, 433, 442, 443) extends to near a closed end of the slit so as to reinforce a neighborhood portion of the closed end of the slit, and wherein the outer column includes a thin part formed, near the closed end of the slit, on the outer peripheral surface thereof so as to allow the diameter thereof to be contracted easily, wherein clearance is formed between the through hole and an outer peripheral surface of the lock pin, so that a bending moment applied to the lock pin is borne only by the flange section (43, 44) when the lock pin is engaged with the steering shaft.