An ink cartridge removably mountable in an image forming apparatus includes a flexible storage member, a pressurization-space formation member, an output port, and an opening-and-closing assembly. The flexible storage member stores ink. The pressurization-space formation member hermetically houses the storage member and forms a pressurization space to which a fluid is supplied between the pressurization-space formation member and the storage member. The output port is connected to the storage member, through which the ink is supplied from the storage member to the image forming apparatus. The opening-and-closing assembly opens and closes between the output port and the storage member by the fluid supplied into the pressurization space.