Search device

A search unit 60 calculates a character-string similarity by acquiring expansion source document data partially matching a search query 70 from a character-string search index 40, determines a relational-data expansion similarity by acquiring expansion destination document data defined to have a relationship with the expansion source document data from a relational-data expansion index 50 and correcting the acquired data by the character-string similarity of the expansion destination document data and relation weight data 80, and outputs a search result 90 arranged in an order of the relational-data expansion similarity.