PURPOSE: To enable even a small and extremely thin printing circuit board to be secured firmly to a conveyor belt and polished properly and automatically by adsorbing the board to the conveyor with an adsorption device.

CONSTITUTION: A printing circuit board P is carried on a conveyor belt 4 and when the board P under carriage reaches the position of an adsorption device 12, the adsorption force thereof reaches the board P via many openings 11 of the conveyor belt 4, and the board P is adsorbed to the conveyor belt 4 by the adsorption force. And the board P under carriage is polished with an abrasive member 7 and rust, scratches, stains and the like are properly removed from the surface of the P. Furthermore, the board P is smoothed, activated, roughness treated and aligned. Even if the printing circuit board P is small and extremely thin, the leading end thereof is free from being entrapped, kicked off and thrown away by the rotating abrasive member 7. Also, the board P is entirely free from being torn off, bent, fractured and damaged otherwise. Consequently, proper and automatic polishing can be ensured.