There is provided an ink cartridge which is formed from an ink-filled ink pack and a hermetic outer shell case for housing the ink pack and which supplies ink to a recording head by means of application of air pressure to a space between the outer shell case and the ink pack. The outer shell case is formed by coupling an upper case and a lower case together. The ink-filled ink pack is housed in the lower case, and the upper case is laid on the lower case from above. The upper and lower cases are hermetically sealed by vibratory welding or heat welding, thus constituting the ink cartridge.