To provide a key insert position lighting device high in general usability and low in cost, and key insert position lighting part structure of a steering locking device.

This key insert position lighting device comprises a flexible, transparent light guide sheet 3 wound and stuck onto the tip part outer periphery of a cylinder case 2 holding a cylinder lock 1 to the center part so as to be rotatory-operated; a light source 5 fixable to the tip part of the cylinder case 2 through a bracket 4; and a flexible reflecting sheet 8 with an irregular reflection surface 6 formed on one face and with an adhesive layer 7 at the back face so as to reflect light reflected from the irradiation surface of the light guide sheet 3 by the light source 5, to this irradiation surface by the irregular reflection surface 6. Irradiation light from the light source 5 is guided to the end face 3a of the light guide sheet 3 exposed to the outside, to visualize a key insert position.