A thumbnail image generating unit generates thumbnail images from a plurality of images having a sequential relation. A thumbnail image displaying unit displays the thumbnail images generated according to the sequential relation. A thumbnail image designating unit receives a designation of a thumbnail image from among the thumbnail images. An enlarging unit generates an enlarged image of a designated thumbnail image. An enlarged image displaying unit displays the enlarged image. A forward-advance designating unit designates a forward advance of the enlarged image displayed by the enlarged image displaying unit according to the sequential relation.