If the validity of authorization information read from a USB key is verified (S1 to S4), use-information that indicates “used” is written in both of the nonvolatile memory and the USB key (S7). In a case of an initial use of an image forming apparatus (Cp=1, S8), a screen for selecting whether to perform a secure format on a hard disk device or not is displayed on a control panel (S9). If an instruction from the control panel indicates performing a secure format (S10), or if the use of the image forming apparatus is not a first time (Cp>1, S8), overwrite process on the hard disk with dummy data device is performed (S13, S14), and a logical format is performed regardless of a selection on the screen (S16).