The ink cartridge has: a cartridge container having a flat box shape; an ink bag that is made of a plastic material or an elastic body, accommodates ink, is disposed in the cartridge container, and has an ink supply port via which the ink is extracted from the ink bag, wherein: the cartridge container has an air connection port by which an interior of the cartridge container in which the ink bag disposed is able to connect to an atmospheric air; the ink bag has a flat shape matching the flat box shape of the cartridge container; the ink bag is provided with a negative pressure generating device which applies impelling force to the ink bag in a direction of expanding a volume of the ink bag to generate a negative pressure inside the ink bag; and the impelling force applied to generate the negative pressure inside the ink bag by the negative pressure generating device, becomes less in a continuous or a stepwise fashion, as a distance from the ink supply port of the ink bag increases.