PURPOSE: To cope with various types of moving device which prevent its end from deflecting by engaging members to be secured over both sidewalls of a body formed in a rectangular trough shape.

CONSTITUTION: This quartz glass form 10 is formed of a quartz glass body 11 formed in a rectangular trough shape and cut out in parallel with a bottom wall 11b at both sidewalls 11a of the ends near the bottom wall 11b, and a quartz glass member 12 to be secured, formed in a semicylindrical shape and engaged over both sidewalls 11a. According to the configuration, since the deflection of the bottom wall is suppressed by both sidewalls, it can prevent the end from deflecting. Further, it can be easily coped with various types of placing devices merely by altering the member. Moreover, if the body is worn, the member can be repeatedly used only by replacing the body.