An ink cartridge 1 attachable to an ink jet printer, includes a liquid chamber 5 for accommodating an ink liquid 4, a liquid supply port 7 to be connected to a liquid receiving portion 2a on the ink jet printer side, a liquid passage 9 for causing the liquid chamber 5 to communicate with the liquid supply port 7, and an ink end sensor 13 forming a part of the liquid passage 9 and serving to detect a presence or absence of the ink liquid 4 in the liquid chamber 5. The liquid passage 9 on a downstream of the ink end sensor 13 is provided with a buffer chamber 15 capable of storing the ink liquid 4 to be supplied to the liquid supply port 7 and supplying the ink liquid in a constant amount after the ink end sensor 13 detects that the liquid is not present. An amount of storage of the liquid in the buffer chamber 15 is set to be substantially 10% of an effective amount of the ink liquid to be accommodated in the liquid cartridge 1.