An ink container connectable with an ink jet head detachably mountable to an ink jet device, the ink container includes a container body; a partition wall dividing an inside of the body into a first accommodating chamber and a second accommodating chamber; wherein the first accommodating chamber contains a negative pressure producing member and is provided with an ink supply opening connected with the ink jet head to supply ink and an air vent portion for communication with the ambience, the ink supply opening being formed in a wall faced to the partition wall; wherein the partition wall is provided with a fine communicating portion which is effective to permit movement of the ink from the second accommodating chamber to the first accommodating chamber and to permit movement of the air from the first accommodating chamber to the second accommodating chamber; and wherein such a portion of the negative pressure producing member as is in a path connecting ink supply opening and the fine communicating portion is more compressed than another portion thereof.