A method of filling an ink cartridge with ink, the ink cartridge being to be mounted on a main body of a recording apparatus and including: a casing in which is formed an ink chamber for accommodating ink; and at least one valve member which is disposed on one side of the casing and which is biased, in an ordinary state, in a direction to close at least one communication passage through which the ink chamber communicates with an exterior of the ink cartridge, the at least one valve member being arranged to be placed in an open state when the ink cartridge is mounted on the main body of the recording apparatus, the method including: forming, at a portion of the casing except for the one side thereof on which the valve member is disposed, an opening through which the ink chamber and the exterior of the ink cartridge communicate with each other; and filling the ink cartridge with ink by introducing the ink into the ink chamber through the opening.