To facilitate assembling works, increase holding force with a towing hook, adapt the wide range of shape alteration of the towing hook, and lower cost involved.

A corrugated tube is employed, which is provided with a plurality of ribs in the circumferential direction, and can be telescopic in the longer direction, and a slit 15 is provided as a protector 13 over the portion of the corrugated tube, which corresponds to the surface side of the curved tip end part 4 of a towing hook 2. After the protector 13 has been fitted in the outer circumference of a straight part 6 from the one side of the flat shaped fixing part 8 of the towing hook 2, and it is moved to the curved tip end part 4 of the towing hook 2 so as to be mounted in place, so that it thereby covers the back face side of the tip end part 4 of the towing hook 2.