Ink-jet printing unit having plate-stacked type printing head and method of producing the same

An ink-jet printing unit for an ink-jet printing apparatus, comprising:

• an ink-jet printing head including a nozzle plate having a multiplicity of nozzle holes which are arranged in at least one row and from which ink is ejected, and a plurality of intermediate plates, which are superposed on the nozzle plate and which provide ink passages communicating with the nozzle holes;
• and
• a head holder which holds the ink-jet printing head,
• wherein the ink-jet printing head has, on an outer side surface thereof, a plurality of reference portions on the basis of which the ink-jet printing head is positioned relative to the head holder in fixing the ink-jet printing head to the head holder, the plurality of reference portions being provided on one of an outer side surface of the nozzle plate and an outer side surface of any one of the plurality of intermediate plates and structured to be brought into contact with a plurality of positioning members when the ink-jet printing head is positioned relative to the head holder, and
• wherein portions of the outer side surface of the ink-jet printing head, which correspond to the positioning members and which exclude the plurality of reference portions, do not protrude outwardly of the plurality of reference portions.