A phototimer detects the dose of an X-ray radiation that has passed through a stimulable phosphor panel, and a stored quantity calculator calculates the quantity of radiation energy stored in the stimulable phosphor panel. An irradiation time ratio setting unit reads an irradiation time ratio from an irradiation time ratio storage unit according to the calculated quantity of radiation energy, and sets the read irradiation time ratio in an erasing unit. Based on the irradiation time ratio, the erasing unit applies erasing light including a radiation in a short wavelength range to the stimulable phosphor panel and thereafter applies erasing light comprising only a radiation in a long wavelength range to the stimulable phosphor panel, thereby erasing a residual radiation image from the stimulable phosphor panel.