an ink jet recording apparatus has a sub tank that supplies ink from an ink cartridge to an ink jet head carried by a reciprocating carriage . the sub tank has an ink container formed of two opposed resin films welded together around their peripheries , and resin sheet members are attached to the ink container over the weld portion for expanding the ink container and restoring it to its original shape after the ink container is deformed by ink flowing in or out of the ink container . the sheet members may be polyimide tape strips or the like that have higher resilience than the material of the ink container and prevent plastic deformation of the ink container due to expansion and compression thereof as ink flows in and out of the ink container .