To efficiently control an image data while taking security in each user into account when a plurality of image data is accumulated in each of a plurality of users.

A controller (method) is provided with an image data storage means for storing the image data, an image data control means for controlling the image data by a directory using a user name and a job name, and for conducting control to allow an access to each job of the corresponding user by inputting the user name, a thumb-nail image generating means for generating a thumb-nail image on at least one page in the image data of the each job by a file name related to the job name, to be stored in the image data storage means, and a control means for controlling a thumb-nail image generated by the file name related to the each job to be perusable in response to an input of the user name from an outside, as to the image data stored in the image data storage means.