PURPOSE: To make clear the luminance difference of gray scale and to provide high-gradation luminance by controlling not only pulse width but also amplitude in order to control the luminance of panel.

CONSTITUTION: When a switch S1 is changed over to a terminal (b), an anode electrode AN of a gas discharge display panel 10 is turned on, a switch S2 is changed over and a cathode electrode is turned on, a cell is discharged. Then, a voltage to be linearly increased from a minimum discharge starting voltage within one horizontal synchronizing period is impressed to the anode electrode AN. In this case, the minimum voltage is defined as 70V and the maximum voltage is defined as 120V. When a voltage VA to be impressed to the anode electrode AN is linearly increased from 70V to 120V within the horizontal synchronizing period, not only the luminance difference of gray level caused by amplitude but also the luminance difference caused by size appear on the display panel, the luminance difference is made clearer and high gradation can be provided.