To prevent lowering of polishing force even in the case of polishing for many hours by mixing abrasive grains for dressing media, in a polishing barrel at the time of polishing a workpiece in a method of polishing the work piece using synthetic resin media formed by mixing abrasives to be cutting edges and compacting them.

At the time of polishing a workpiece W, a top part 18b of a cover body 18 is opened to charge the workpiece W, media M and abrasive grains S on a rotary table 3 of a polishing barrel 1, and the top part 18b is closed. A motor 6 is operated to make the workpiece W, media M and abrasive grains S turn and flow by the rotation of a rotary table 5 and to polish the workpiece W by the media M while dressing with the abrasive grains S. That is, even though abrasive powder generated during polishing adheres to the surface of the media M and is going to embed cutting edges, the cutting edges of the media M are generated and exposed because of dressing performed by the abrasive grains S, and the workpiece can be polished without lowering polishing force. The abrasive powder generated during polishing is sucked by a dust arrester 14 and eliminated.