PURPOSE: To enhance the gas-tightness of a barrel tank to prevent the inside of a barrel processing machine from being polluted by enclosing shape-memorizing alloy in one or both of barrel cover fitting areas so as to realize tight adhesion of fitting areas owing to temperature rise at the barrel tank being polished.

CONSTITUTION: Workpieces, polishing material and water, and further compound as required are placed inside a barrel tank 6, and a barrel cover 11 is laid thereon through screwing process by means of a male screw 'a' consisting of groove streaks 7 and ridge streaks 8 and a femals screw b consisting of ridge streaks 9 and groove streaks 10. When a polishing work is carried on, the temperature and pressure inside the barrel tank 6 rise probably causing leak of water under poor gas-tightness. However, when the temperature inside the barrel tank 6 reaches approximately 50°C, shape memorizing alloy 1a buried on the side of barrel 6 is deformed by expansion, while shape memorizing alloy 1b burried on the side of cover 11 is deformed by contraction so as to enhance gas-tightness. Meanwhile, the temperature inside the barrel tank 6 drops quickly beyond 50°C after the end of polishing process, so as to facilitate opening of the cover. Thus, possibility of water leak is eliminated to prevent the inside of a barrel processing machine from being polluted.