Ink jet print head and ink jet printing apparatus having a plurality of slits formed in a heater substrate mounting surface

The present invention is intended to alleviate stresses that occur in a bonding surface between the heater substrate and the base plate due to effects of heat history in the ink jet print head manufacturing process and to heat produced during the printing operation. To this end, the present invention provides an ink jet print head comprising: a heater substrate formed with heaters to generate thermal energy for ejecting ink; and a base plate mounted to that part of a surface of the heater substrate in which the heaters are not formed; wherein a plurality of slits each of which extends in a direction perpendicular to a direction of an array of the heaters formed in the heater substrate are formed in a heater substrate mounting surface of the base plate at predetermined intervals in a direction of an array of the heaters.