An ink cartridge using an ink bag capable of being mounted in a carriage, comprising: a container having a body unit 1 and a cover unit 3 to form an internal space therebetween, at least one of said body unit and said cover unit being provided with valves 10 and 11 openable for communication between the internal space of said container and the atmosphere according to pressure change in said container; a cap 21 connecting with an ink supply needle of a recording head mounted in a carriage; and an ink bag, the periphery of which is held by said cover unit 3 and body unit 1. A constant negative pressure can be maintained by valves 10 and 11, and the periphery of ink bag 20 is held by body unit 1 and cover unit 3, ensuring as constant a shape as possible and preventing pressure changes caused by oscillation.