PURPOSE: To obtain the amount of stable coating by touching a glass mixture layer which moves to be loaded on the circumferential surface by means of roller rotation and a coated material and cutting off the layer in the direction of thickness.

CONSTITUTION: A roller frame 21 for coating mixture is provided in a container 12. In this frame 21, a stainless roller 23 is secured on an axis of rotation 22 which is axially racked between both end plates of the container so as to freely rotate and the upper part of the roller slightly protrudes from the upper opening section 12 of the container 12. A knife-shaped thickness regulating piece 25 is mounted inside the front side plate 14 of the container 12 for the circumferential surface of the roller 23 through a support mechanism 26 so as to freely advance and retreat and a wire 27 where preset tensile force is applied through a pulling jig 28 to a support plate 29 which is secured on the end plate 15 of both ends is hung above the roller 23 in parallel to the axis of rotation 22. This can obtain the amount of stable coating.