to an ink bag and fig3 is a partially sectioned view of a position determining engaging mechanism for the ink outlet piece the ink bag designated by reference numeral 1 is constructed using a laminated aluminum film which is laminated with two films such that the outside of the ink bag is lined with e g a nylon film while the inside of the same is lined with e g a polyethylene film in order to improve the gas barrier property of the ink bag these films are thermally fused together along the outer peripheral edge of the ink bag 1 to conduct ink out of the ink bag 1 to the outside an ink outlet piece 2 is integrated with the ink bag 1 by thermal fusion on the front side as seen in fig1 the ink outlet piece 2 is molded of a plastic material as shown in fig2 the rear part of the ink outlet piece 2 i e the joint location where the ink bag 1 is thermally fused with the ink outlet piece 2 is constructed in a leaf shaped configuration such that the central part exhibits an convex arc having a large radius of curvature and the opposite ends exhibit an concave arc having a large radius of curvature with this construction a gap between the ink bag 1 and the ink outlet piece 2 is fully filled with molten material during a thermal.