To facilitate the confirmation of the classification result of image data classified into hierarchized holders.

Image data S0 are classified into a plurality of hierarchized holders and stored in a recording means 12. A user designates the display mode of each holder from an input means 14 when displaying a classification result display screen for image data S0 on a monitor 11. Concretely, the user designates a first mode for giving the thumbnail image of the image data classified to the holders followed by displaying or a second mode for displaying the thumbnail image of the image data classified to the holders with respect to each holder. The designation result is stored in the recording means 12 as display mode information D0. When the display of the classification result display screen is instructed, the classification result display screen is displayed on the monitor 11 in reference to the display mode information D0.