A steering lock device comprising: a cover; a frame covered with the cover; the frame being provided with a rod guide hole; a lock member arranged in the rod guide hole freely slideably between a steering lock position and a steering lock release position, the rod guide hole being provided in the frame; and an auxiliary lock mechanism operable in response to an external force applied to the cover so as to hold the lock member at the steering lock position at an illegal unlocking, the auxiliary lock mechanism including an auxiliary engagement portion provided on the lock member, an auxiliary lock member that is arranged in the frame freely slideably between an auxiliary lock position and an auxiliary lock release position, and is urged by an urging member to a lock position side of engaging with the auxiliary engagement portion, and a holding member having one end fixed to the cover, in which, in a state where the cover is assembled to the frame, a tip end of the holding member makes engagement with a holding/receiving portion of the auxiliary lock member located at the auxiliary lock release position, and holds the auxiliary lock member at the auxiliary lock release position, and in an event where the cover relatively moves from the frame, the engagement with the holding/receiving portion is disengaged; characterized in that an inclined portion (95, 95a, 95B) is formed on either one of an inside of the opening edge of the cover and an outside of an opening edge of the frame, and an inclination receiving portion (96, 96a, 96B) is formed on the other of the inside of the opening edge of the cover and the outside of the opening edge of the frame, and that the cover has an urging force toward the inside of the opening edge of the cover. a cover; a frame covered with the cover; the frame being provided with a rod guide hole; a lock member arranged in the rod guide hole freely slideably between a steering lock position and a steering lock release position, the rod guide hole being provided in the frame; and an auxiliary lock mechanism operable in response to an external force applied to the cover so as to hold the lock member at the steering lock position at an illegal unlocking, the auxiliary lock mechanism including an auxiliary engagement portion provided on the lock member, an auxiliary lock member that is arranged in the frame freely slideably between an auxiliary lock position and an auxiliary lock release position, and is urged by an urging member to a lock position side of engaging with the auxiliary engagement portion, and a holding member having one end fixed to the cover, in which, in a state where the cover is assembled to the frame, a tip end of the holding member makes engagement with a holding/receiving portion of the auxiliary lock member located at the auxiliary lock release position, and holds the auxiliary lock member at the auxiliary lock release position, and in an event where the cover relatively moves from the frame, the engagement with the holding/receiving portion is disengaged; characterized in that an inclined portion (95, 95a, 95B) is formed on either one of an inside of the opening edge of the cover and an outside of an opening edge of the frame, and an inclination receiving portion (96, 96a, 96B) is formed on the other of the inside of the opening edge of the cover and the outside of the opening edge of the frame, and that the cover has an urging force toward the inside of the opening edge of the cover.