PROBLEM TO BE SOLVED : To provide an information retrieval apparatus enabling a reader of information decide easily and surely whether the information retrieved is important information for the reader himself/herself.SOLUTION : The information retrieval apparatus is constituted, when retrieving property information regarding to a piece of real estate satisfying a retrieval condition designated by a certain user, to calculate a degree of fitness which indicates how each piece of property information satisfies the retrieval condition based on a calculation function for a degree of fitness for the user. The apparatus is also constituted to enable each user change the form of its own calculation function for the degree of fitness.