A steering locking device (1, 1A, 1B, 1C) includes: a locking member (6) including a first face (B) parallel to an axial direction of a steering shaft, a second face (C) perpendicular to the first face (B), and a protrusion (62) protruding from the second face (B); and a sliding plate (91) extending from the first face (B) in a plate thickness direction (D) of the locking member (6), arranged outside the first face (B), and engageable with the protrusion (62).