PURPOSE: To make it possible to prevent from stumbling over a treadboard when going up a staircase and confirm visually a nosing with ease and manufacture at a low cost. CONSTITUTION: A front end face is tapered so that the lower edge of the front end face may move back from the upper edge of the front end face, which makes it difficult for the tip of a toe to come in contact with the bottom of a treadboard 10. When the tiptoe touches on the front, it is so guided that people may walk along the tapered surface, thereby preventing people from stumbling. A plastic sheet 12, which prints a belt-like mark 12a is pasted on the treadboard wherein the mark 12a clearly indicates the location of a nosing of the treadboard. Compared with the prior treadboard where a different member from the tread main body is marked and fixed with the main body, the application of this new mark 12a makes it possible to omit treatment or work required to mount the other member to the treadboard and hence reduce construction cost.