To provide a quick image retrieval method convenient for users, which generates and displays image data for thumbnails in two stages of minute sizes.

An image processor generates a multi-valued reduced image and a binary reduced image from an inputted original image and is provided with a storage means for storing the generated multi-values reduced image and binary reduced image therein, an index information storage part for storing link information between the stored original image and the multi-valued reduced image as well as the binary reduced image, a display means, and a selection means, and the image processor is provided with a control means which refers to the index information storage part to display other corresponding images at the time of image selection by the selection means with one of the original image, the multi-valued reduced image, and the binary reduced image displayed on the display means.