A technique which enables improvement of luminance and reduction of consumption power in a sustain discharge driving of a four-electrode structure PDP, particularly, by devising driving method to Z electrodes. In this plasma display device, a sustain discharge by a method to apply a narrow pulse to the Z electrode and a method to apply a fixed potential to the Z electrode are switched according to a judgment of range of display load ratio in driving sustain discharge from a controller and driver to the PDP and used.