To use a polishing barrel made of a polyurethane resin which can be mounted and demounted easily, and is also expanded by the heating following the polishing work.

On the peripheral edge of a rotary disk 7 which rotates a polishing barrel by supporting it, plural supporting arms are planted at specific intervals, so as to form a barrel holding space to fit playable to the polishing barrel in their inside. In the necessary supporting arm 8, a lock mechanism 9 having a locking part 13a to engage and a disengage with the outer periphery of the polishing barrel, which is fitted to this barrel holding space, is provided so as to clamp the polishing barrel in this barrel holding space.