PURPOSE: To reduce a time for mounting and removing a tank so as to improve machining efficiency, by engaging protrusions, provided on an external wall of the barrel tank fitted to a barrel case, with notches provided in an outside wall of the barrel case and increasing the engagement force by turning motion so as to prevent the barrel from disengaging.

CONSTITUTION: A work and an abrasive material, if necessary, water and a compound are placed in a barrel tank 11, and a barrel cover is mounted to be capped. Next, the barrel tank 11 is fitted into a barrel case 15 so that protrusions 14 of the tank 11 are fitted to be engaged with vertical parts 16 of notches 18 in the barrel case 15, and if a bottom part of the barrel tank 11 is completely supported onto a supporting bed, a turret 19 is driven, both revolving the barrel tank 11 integrally with the case 15 in the direction A around an axis of the turret and rotating the barrel tank on its axis around a barrel shaft 20 in the direction C, thus the planetary turning barrel machining is performed. Then as a turning speed of the turret increases, the adapted pressure of the protrusion 14 to the notch 18 increases, thus the barrel tank 11 can be prevented from coming out of the case 15. Such simple constructon can simplify the work further reduce a time of the work.