PURPOSE: To realize a glass surface layer with sufficient adhesion to a material and smoothness of the surface improved to improve the hardness, smoothness and wear resistance of the material.

CONSTITUTION: A rotary drum 2 for a VTR is rotated to form a molten layer 14 on a drum part 4 by a plasma discharge from an electrode 8. A water glass composition is discharged on the molten layer 14 from a nozzle 10 to form a water glass layer 16, and the molten and half-molten parts of the molten layer 14 and the water glass layer 16 are collapsed by a roll 12 and plastically deformed. The molten layer 14 is cooled by the water glass layer 16 which is heated and converted into a glass layer 18. The glass layer 18 having sufficient hardness is extremely smooth, and the surface good in dimensional precision is obtained. Meanwhile, since a mixed layer of glass and metal is formed, the glass layer 18 is firmly bonded to the drum part 4 and durable to the wear of the VTR tape due to its wear resistance, and the wear of the tape is suppressed by the nonporous and extremely smooth surface.