A reliable ink cartridge that reduce printing nonconformity even during high speed inkjet-recording with multiple nozzles by alleviating rapid external impact applied from the outside of the ink cartridge. Within a casing of an ink cartridge, a flexible bag forming an ink reservoir is accommodated. Between the surface of the flexible bag where a sheet member is bonded and a wall surface of the casing, a stress damping chamber is provided. The stress damping chamber communicates with the atmosphere outside the ink cartridge via an orifice formed on a wall surface of the casing.