An ink cartridge takes the form of a bag, and is formed out of a laminate which includes films laminated together. Compressive stress exists in one of the films. Therefore, when a hollow needle pierces the bag, the stress causes this film to function in such a manner as to block the pierced hole. This brings the film into close contact with the needle, preventing ink leakage securely. It is also possible to prevent the cracks developed in the laminate by external injuries from progressing. It is possible to form the laminate by bonding a plurality of films having different coefficients of thermal expansion together at high temperature, and cooling the bonded films. It is possible to form the bag by heat-sealing the laminate.