An image search system for determining a similarity of an image whose feature are represented by either one of image features amounts, a color distribution features or a frequency distribution features, to search for a similar image, including a to-be-searched image features storage unit for referring to data of an image features amount of each image to be searched, an inquiry image features input unit for receiving input of data of an image features amount of an inquiry image, a data processing unit for converting a kind of an image features amount of an image set to be an object whose kind of image features amount is to be changed to make a kind of image features amount of each image to be searched and a kind of image features amount of the inquiry image be coincident with each other, and a similarity calculation unit for comparing the image features amount of the inquiry image and the image features amount of each image to be searched based on the converted image features amount and determining a similarity of each image to search for a similar image.