An image processing apparatus capable of managing easily secret information even with detachably attaching an external memorizing device, includes an ID (plug and play ID) retrieving unit for retrieving ID from the connected memory, a user information storing unit for storing user information, an active memory information storing unit for storing the retrieved ID with corresponding to the respective users, a memory use judging unit for judging as to whether the memory is usable based on the ID retrieved from the connected memory and on the ID stored in the active memory information storing unit, and a data writing controlling unit for writing data to the memory judged as usable.