A device for determining interest includes a storage portion configured to store, on a user-by-user basis, a co-occurrence frequency in correlation with a user, the co-occurrence frequency indicating how many times a pair of words is used in a same cluster of a first document, on a pair-by-pair basis, to which the user gained access previously; a designating portion configured to allow a person who is to conduct a search to designate a second document and any one of the users; and a determination portion configured to determine that, among the pairs, a pair which is used in a same cluster of the designated second document and which also satisfies a predetermined condition of the co-occurrence frequency corresponding to the designated user is a particular pair in the second document which is probably of high interest to the designated user.