The image forming apparatus of this invention comprises an image processing unit that has a storage device capable of storing image data, and processes and outputs the image data stored in said storage device; and a data protection unit that sets security levels respectively for time slots which are scheduled in advance. The security levels are set high in a time slot in which said image forming apparatus is less frequently used and set low in a time slot in which said image forming apparatus is frequently used, and restrictions are placed on the use of said image data as the security level is high.