1. An information retrieval device for retrieving information matching a user preference from an aggregation of retrieval target, including: vectorizing means for generating a feature vector of each piece of the retrieval target; clustering means for clustering each piece of the retrieval target into a plurality of clusters based on the feature vector thereof; representative vector generating means for generating a representative vector of each of said clusters; preference importing means for urging the user to input the preference regarding the retrieval target and importing input preference information; query building means for building a query based on said input preference information; retrieval target narrowing means for comparing the representative vector of each of said clusters and the query, thereby narrowing the clusters to be retrieved into at least one cluster of which similarity is high; retrieval means for comparing the feature vector of retrieval target belonging to said retrieval target cluster and said query, thereby extracting the retrieval target of which similarity is high; and retrieval result outputting means for presenting a result of said retrieval to the user.