An ink tank for being installed in an ink jet recording apparatus to supply ink thereto, including an ink storage portion, one side surface of a casing of the ink tank in which side surface an opening for supplying ink to the apparatus is formed, and a joint member for joining the one side surface to the apparatus by engaging with a connection member of the apparatus. The joint member has a welding portion for being welded to the one side surface along a peripheral portion of the opening, the welding portion corresponding to the peripheral portion; and a hollow portion forming a positioning hole for inserting therein and engaging therewith the connection member for determining a relative position of the apparatus and the one side surface. The hollow portion is provided on the outside of the welding portion and abuts to the one side surface without being welded.