Sustain pulses are alternately applied to a pair of display electrodes of discharge cells provided in a plasma display panel (PDP) to generate a sustain discharge to display an image on the PDP. The sustain pulses include two-crests discharge voltage waveforms having a first maximum and second maximum values, in which discharges are generated twice in a half cycle. After applying a sustain pulse having a one-crest discharge voltage waveform to a pair of display electrodes, a predetermined number of sustain pulses of two-crests discharge voltage waveforms are consecutively applied. A time, from applying a second sustain pulse of a two-crests discharge voltage waveform to clamping a voltage of the second sustain pulse to the second maximum value, is made longer than a time, from applying a first sustain pulse of a two-crests discharge voltage waveform to clamping a voltage of the first sustain pulse to the second maximum value.