from the washing machine the motor 3 and the motors 20 are started the curved glass plate 5 is again placed on the endless belts 2 the curved glass plate 5 moves rearward toward the buff grinders 23 a detergent such as an alumina solution etc is sprayed on the curved glass plate 5 so that a water screen of the detergent is formed on the curved glass plate 5 the curved glass plate 5 reaches the buff grinders 23 the front edge of the curved glass plate 5 abuts against the lower side surfaces of the sponge buffs 22 of the rotating buff grinders 23 the sponge buffs 22 deform to allow the curved glass plate 5 to get under them the curved glass plate 5 moves rearward while the sponge buffs 22 of the rotating buff grinders 23 are uniformly pressed against the upper surface of the curved glass plate 5 thus the upper surface of the curved glass plate 5 is washed by the rotating buff grinders 23 and the stains guard sheet traces yellowed spots etc are removed from the upper surface of the curved glass plate 5 the areas between the buff grinders 23 disposed on the front transverse beam 9 and not washed when the curved glass plate 5 passes by the front transverse beam 9 are washed by the buff grinders 23 disposed on the rear transverse beam 9 since the buff grinders 23 on the rear transverse beam 9 are staggered in the transverse direction relative to the buff grinders 23 disposed on the front transverse beam 9 thus the entire upper surface of the curved glass plate.