PURPOSE: To reduce an assembling man-hour by eliminating forming of a lower hole at an ink absorber when an ink residue sensing pin is press injected in an ink tank of an ink jet recorder which contains the absorber.

CONSTITUTION: A cross hole for a driver is provided at an end of a press injecting bit mount 1a of an ink residue sensing pin 1, the pin 1 is press injected in an ink tank 3 while rotating the pin 1 by a driver, and its submerged part 1c is embedded in a sponge (ink absorber) 4 in the tank 3. A self-tapping screw lb of the pin 1 is bitten to an outer wall of the tank 3, and the pin 1 is fixed.