A steering locking device comprising: a locking member arranged in a housing to be slidable between a locked position and an unlocked position, the locking member at the locked position being engaged with a steering shaft to prevent rotation of the steering shaft and at the unlocked position being separated away from the steering shaft to allow the rotation of the steering shaft, the locking member including a first face parallel to an axial direction of the steering shaft, a second face perpendicular to the first face; a sliding plate held to be slidable between an engaged position and a disengaged position and urged toward the engaged position, the sliding plate at the engaged position being engaged the locking member located at the locked position and at the disengaged position being separated away from the locking member to allow sliding of the locking member; and a holding portion arranged to be attachable to and detachable from the housing, the holding portion attached to the housing being configured to engage with the sliding plate located at the disengaged position to hold the sliding plate at the disengaged position, wherein when the holding portion and the sliding plate are disengaged from each other, the sliding plate is moved from the disengaged position to the engaged position and engaged with the locking member to prevent movement of the locking member from the locked position to the unlocked position, characterized in that the locking member includes a protrusion (62,74b,79) protruding from the second face, and the sliding plate at the engaged position being engaged with the protrusion (62,74b,79) of the locking member. a locking member arranged in a housing to be slidable between a locked position and an unlocked position, the locking member at the locked position being engaged with a steering shaft to prevent rotation of the steering shaft and at the unlocked position being separated away from the steering shaft to allow the rotation of the steering shaft, the locking member including a first face parallel to an axial direction of the steering shaft, a second face perpendicular to the first face; a sliding plate held to be slidable between an engaged position and a disengaged position and urged toward the engaged position, the sliding plate at the engaged position being engaged the locking member located at the locked position and at the disengaged position being separated away from the locking member to allow sliding of the locking member; and a holding portion arranged to be attachable to and detachable from the housing, the holding portion attached to the housing being configured to engage with the sliding plate located at the disengaged position to hold the sliding plate at the disengaged position, wherein when the holding portion and the sliding plate are disengaged from each other, the sliding plate is moved from the disengaged position to the engaged position and engaged with the locking member to prevent movement of the locking member from the locked position to the unlocked position, characterized in that the locking member includes a protrusion (62,74b,79) protruding from the second face, and the sliding plate at the engaged position being engaged with the protrusion (62,74b,79) of the locking member.