A processor of a server includes: a keyword generator that narrows object images from video based on both activity information on the activity history of a user and a first level of narrowing down and generates candidate keywords, as candidate comments, by generating a candidate keyword for each of the images; an identifier that identifies one or more target keywords from among the candidate keywords generated by the keyword generator based on both the activity information and a second level of narrowing down; a comment generator that generates, for each of the one or more target keywords, a comment related to each target keyword; and an adjuster that adjusts the first level of narrowing down in the keyword generator and the second level of narrowing down in the identifier in accordance with processing information on processing performable by the keyword generator and processing performable by the identifier.