When aging is performed by applying aging voltage to a data electrode, a scan electrode, and a sustain electrode via respective inductors (301, 401, 302, 402, 303, 403) coupled to the electrodes, frequency of a ringing waveform included in an aging voltage waveform applied to the data electrode is set in a range of ½ to 2 times frequency of a ringing waveform included in an aging voltage waveform applied to the scan electrode. With the method above, the time required for aging is significantly shortened, and the aging with high efficiency in electric power is realized. Instead of using inductors (301, 302, 303) including a coil, controlling the length of lead wires (401, 402, 403) can also obtain desired inductance.