Abstract

An ink tank suitable for use in an ink-jet recording apparatus, comprises a closed ink bladder of a flexible material, the ink bladder being formed by assembling two double-folded sheets with each other or by folding a single sheet with the peripheral matched portions of the folded sheets or sheet adhered to each other, and the larger sheet or said single sheet includes a plug member sealingly attached thereto at a position adjacent to the folded portion of the larger sheet or adjacent to the corresponding portion of said single sheet, said plug member having an ink outlet port. In an ink-jet recording apparatus comprising such a closed ink bladder of a flexible material for supplying ink to a recording head, the plug member mounted on said ink bladder includes a pair of upper and lower electrodes exposed to the ink in said ink bladder, inwardly extending ribs disposed on the opposite sides of said plug member and effective to prevent said ink bladder from completely collapsing, and detection means for sensing a change in electrical resistance between said electrodes to detect the residual amount of ink within said ink bladder when a gas enclosed in said ink bladder reaches between said ribs.