In the aging process performed by applying a voltage having an alternate voltage component between a scan electrode and a sustain electrode, an erase discharge occurs in succession to an aging discharge. According to the aging method of the present invention, an erase discharge-suppressing voltage is applied to at least any one of the scan electrode, the sustain electrode, and the data electrode. Although the erase discharge repeatedly occurs in the wake of the aging discharge, the erase discharge-suppressing voltage suppresses the ones that occur when the scan electrode takes voltage level higher than the sustain electrode.