1. An image evaluation device comprising: an image feature extraction unit that extracts image features from a plurality of images; an evaluation information acquisition unit that acquires evaluation information, the evaluation information containing results of evaluations of the images performed by users including a subject user; a generation unit that generates relational information based on the image features and the evaluation information, the relational information showing relationship between the images, the users, and image feature groups into which the image features are classified, the relational information including image feature group importance degrees; and an image social importance calculation unit that calculates an image social importance degree of each image based on the relational information generated by the generation unit, each image social importance degree showing a degree of importance to the subject user of the corresponding image, wherein the evaluation information contains evaluation numbers respectively corresponding to the image feature groups, each evaluation number indicating the number of evaluations performed by any of the users on images containing any image feature belonging to the corresponding image feature group, and the image social importance calculation unit calculates the image social importance degree of each image based on a sum of the image feature group importance degrees of the image feature groups that the image features contained in the corresponding image belong to.