An objective of the present invention is to make a search for illegal (illegitimate) content more efficient. The illegitimate content relates to content posted by an unauthorized user without a legitimate ownership of the content. An illegitimate content search device according to the present invention comprises: a query generation dictionary storage part for storing a query generation dictionary for generating a search query used in searching for illegitimate content; a query generation dictionary creation part for extracting, from a title of illegitimate content, associated wording being associated with wording included in a title of legitimate content, and registering the extracted associated wording in the query generation dictionary for generating the search query used in searching for the illegitimate content; and a search query generation part for generating the search query using the associated wording registered in the query generation dictionary.