An ink cartridge includes an ink containing section including an ink absorbing body made of a porous material for retaining ink. The ink cartridge satisfies 200≦N·R≦320, where N is the cell density, expressed in the number of pores per inch, of the ink absorbing body before the ink absorbing body is contained in the ink containing section; and R is a compressibility, which is a volume ratio of the ink absorbing body when the ink absorbing body is contained in a compressed state in the ink containing section to the ink absorbing body before the ink absorbing body is contained in the ink containing section. With this configuration, it is possible to (1) preventing ink leakage that is caused when the ink cartridge is inserted or detached, (2) realize stable supply of the ink when continuous ejection is performed, and (3) achieve effective utilization of the ink cartridge volume, thereby realizing an ink cartridge and an image forming apparatus which provide design indices for the ink absorbing body in accordance with properties of the ink.