Abstract: In a display unit comprising a plate-shaped display panel with X-Y matrix electrodes consisting of two groups of electrodes, X-axis electrodes and Y-axis electrodes, display signals are applied to the X-Y matrix electrodes, a.c. current is applied to at least one group of electrodes one after another, and the phase of the a.c. current is compared with that of the output of an input pen having means for detecting the magnetic flux induced by the a.c. current, so that the position of the input pen on the display panel is detected from the result of the comparison.