Brightness feature information on the brightness of an image to be processed is extracted, and color feature information on the color of the image is extracted. A determination unit determines whether color information of the image to be processed is sufficient. When color information of a reference comparison image is sufficient as a result of determination, a color feature information comparison unit performs a similarity comparison between color feature information of the reference comparison image and that of a target comparison image. When the color information of the reference comparison image is insufficient, a brightness feature information comparison unit performs a similarity comparison between brightness feature information of the reference comparison image and that of the target comparison image. A retrieval result display displays an image serving as a retrieval result on the basis of the comparison result.