PURPOSE: To prevent residence of a work on the inner wall of a tank, to reduce production of a notch owing to collision of the works with each other, and to improve a yield by providing an air device to uniformly inject air bubbles through the lower surface of the whole periphery of a microgap of the inner peripheral surface of a fixed tank.

CONSTITUTION: A plurality of holes 2 are formed in the under surface of a fixed tank 1 and compressed air is fed in the holes 2 through a filter regulator 3, a solenoid valve 4, a flow rate regulating valve 5, and a check valve 6. The compressed air produces air bubbles 8 in a polishing tank and enters a barrel tank through a gap α between the fixed tank 1 and a rotary tank 7. The number of the holes 2 being a number enough to allow uniform injection of the air bubbles 8 through the gap α are formed. Thereafter, works and polishing water are charged in the barrel tank, an amount of the air bubbles 8 is regulated by the flow rate regulating valve 5. Through rotation of the rotary tank 7, barrel polishing is executed without residence of the works on the inner wall of the fixed tank 1 and the upper surface of the rotary tank 7.