PURPOSE: To prevent a slip even when a surface is wetted with water such as rain or the like by applying non-skid paint to the surface of a deck plate on which a flat part and an upright web are alternately formed, thereby applying a non-skid treatment.

CONSTITUTION: While a belt-shaped steel plate in the shape of roll is being unwound and carried by a conveyor belt, the plate is folded and bent by a roll forming process to form a deck plate 1, and washing liquid is sprayed onto the surface of the plate to remove attached oil, dusts, and moisture therefrom. Next, the plate undergoes a heating treatment at a temperature of 70-110°C and is dried and then a non-skid paint prepared by mixing a non-skid material composed of particles 100μm or less in diameter, pigments, water or solvent into resins such as water-soluble alkyd resin varnish, acrylic resin emulsion is applied to the surface of the plate and dried, thereby applying a non-skid treatment thereto. T-shaped webs 3 are oriented upwards and embedded in concrete 8 placed on the deck plate 1. And the deck plate 1 is utilized as a structural material.