A plurality of image data are stored in a hard disk device in correspondence with their image feature amounts. An image is input using an input window. A CPU computes the image feature amount of the input image. The CPU also computes image similarity on the basis of the computed image feature amount and those of image data stored in the hard disk device. A list of image data as search results are displayed on a display unit on the basis of the computed image similarity. Image data stored in the hard disk device are read out into the input window.