PURPOSE: To protect workers from accidents such as falling by slipping on a scaffold and also to prevent damage of tiles in such a roof tile laying work as painting building surface.

CONSTITUTION: The treadboard supporting device is composed of a treadboard base tool 11, on which a treadboard 31 is placed, and a supporter 1 for supporting the treadboard base tool on the roof tile. The supporter has a supporting frame 5 provided behind a body for forming a tile end stopper 4 by bending its front end downwards. The treadboard base tool is equipped with a horizontal supporting base and right and left side walls 13 continuing to the horizontal supporting base. A treadboard stopping protrusion 15 is provided on the end at the lower part of the horizontal supporting base and the bottom edge of each side wall is tilted in response to the tilting of the tile roof while steps corresponding to the thickness of the tile is provided on the bottom edge of each side wall.