PURPOSE: To ensure a constant ink supply by contacting a pair of electrodes to the lower portion of an ink absorber feeding an ink to a printing wire in order to increase the detection sensitivity around the most desirable ink absorbing quantity.

CONSTITUTION: A sponge type ink absorber 5A is stored in an ink chamber 30 positioned at the tip portion of a printing head of a wire dot printer. The vertical edges of the right side of the ink absorber 5A are respectively cut away in an L shape to form steps 20, 21. At the lower portions of the steps 20, 21, a pair of electric rods are provided in such a manner as to press the steps 20, 21 from both sides. When the pressure is comparatively increased, a stable detection is obtainable by minimizing the time series change of the contact pressure as well as the variation of various articles.