An ink jet head includes a recording element substrate includes a plurality of ink supply ports and a supply port partition between adjacent ink supply ports; a substrate supporting portion supporting the recording element substrate at a back side thereof, the substrate supporting portion including ink supply passages corresponding to the ink supply ports and a supply passage partition corresponding to the supply port partition; a sealing material contacted to a side surface of the recording element substrate and to the substrate supporting portion; adhesive material fixing the opening partition and the supply passage partition to each other, wherein back sides of opposite ends of the recording element substrate with respect to an arranging direction of the ink supply ports are unfixed by the adhesive material to the substrate supporting portion.