A steering lock device, comprising: a lock member arranged to be displaceable between a steering lock release position at which it is accommodated within a guide hole formed in a guide part that constitutes a frame and a steering lock position at which its tip protrudes from the guide part, the lock member having a hanger and a lock body that are disengageably linked; an auxiliary lock mechanism that comprises: an auxiliary lock receiving part arranged on either one of the guide part or the lock body, an auxiliary lock member arranged on the other of the guide part or the lock body to be biased toward the auxiliary lock receiving part, and arranged to be displaceable between an auxiliary lock position at which it engages with the auxiliary lock receiving part and an auxiliary lock stand-by position at which it does not engage with the auxiliary lock receiving part, and a holding member that engages with the auxiliary lock member and holds the auxiliary lock member in the auxiliary lock stand-by position, wherein the auxiliary lock mechanism restricts displacement of the lock member positioned in the steering lock release position by the auxiliary lock member moving to the auxiliary lock position to engage with the lock member when engagement of the holding member and the auxiliary lock member is released; and a fragile part provided on the guide part at a position that overlaps with a linkage portion between the hanger and the lock body of the lock member positioned in the steering lock release position, the fragile part being set to have lower load resistance than other positions of the frame, wherein a holding hole which is formed in the guide part and in which the holding member is arranged is set to have a larger dimension on the fragile part side along a given direction that an external load enters than a dimension on the auxiliary lock member side, wherein in a case that external force is applied to the frame, the holding member tilts to release the engagement between the holding member and the auxiliary lock member, a lock member arranged to be displaceable between a steering lock release position at which it is accommodated within a guide hole formed in a guide part that constitutes a frame and a steering lock position at which its tip protrudes from the guide part, the lock member having a hanger and a lock body that are disengageably linked; an auxiliary lock mechanism that comprises: an auxiliary lock receiving part arranged on either one of the guide part or the lock body, an auxiliary lock member arranged on the other of the guide part or the lock body to be biased toward the auxiliary lock receiving part, and arranged to be displaceable between an auxiliary lock position at which it engages with the auxiliary lock receiving part and an auxiliary lock stand-by position at which it does not engage with the auxiliary lock receiving part, and a holding member that engages with the auxiliary lock member and holds the auxiliary lock member in the auxiliary lock stand-by position, wherein the auxiliary lock mechanism restricts displacement of the lock member positioned in the steering lock release position by the auxiliary lock member moving to the auxiliary lock position to engage with the lock member when engagement of the holding member and the auxiliary lock member is released; and an auxiliary lock receiving part arranged on either one of the guide part or the lock body, an auxiliary lock member arranged on the other of the guide part or the lock body to be biased toward the auxiliary lock receiving part, and arranged to be displaceable between an auxiliary lock position at which it engages with the auxiliary lock receiving part and an auxiliary lock stand-by position at which it does not engage with the auxiliary lock receiving part, and a holding member that engages with the auxiliary lock member and holds the auxiliary lock member in the auxiliary lock stand-by position, wherein the auxiliary lock mechanism restricts displacement of the lock member positioned in the steering lock release position by the auxiliary lock member moving to the auxiliary lock position to engage with the lock member when engagement of the holding member and the auxiliary lock member is released; and a fragile part provided on the guide part at a position that overlaps with a linkage portion between the hanger and the lock body of the lock member positioned in the steering lock release position, the fragile part being set to have lower load resistance than other positions of the frame, wherein a holding hole which is formed in the guide part and in which the holding member is arranged is set to have a larger dimension on the fragile part side along a given direction that an external load enters than a dimension on the auxiliary lock member side, wherein in a case that external force is applied to the frame, the holding member tilts to release the engagement between the holding member and the auxiliary lock member,