To protect a lower plate by a method wherein first and second plates each having a through-part are laminated together, and the plates are securely nipped by the head part and the extension part of the fixing tool mounted on the through-part.

For example, a notch part 2a is formed through in the direction of the thickness of a notch part 2a in one end of a cover 2 made of concrete of a U-gutter 3 and a long groove-form through-hole 1a is formed in the central part of a laying plate 1 made of resin. The laying plate 1 is placed on the cover 2, and the through-hole 1a is positioned on the notch part 2a. A fixing tool 4 is provided, comprising a plate- form head part 4a; a screw part 4b being a male screw; a cylindrical part 4c in which a female screw is formed; and an extension part 4d extending from the cylindrical part 4c to an external part. The fixing tool 4 is mounted in a manner to extend from the internal part of the through-hole 1a to the interior of the notch part 2a, the laying plate 1 and the cover 2 are nipped between the head part 4a and the extension part 4d, and a screw part is securely fastened. This constitution reliably protects the cover by preventing the occurrence of displacement in a position of the laying plate, improves safety during the passage of a vehicle, and prevents the occurrence of a thief of the laying plate or the like.