1. A configuration information management apparatus which manages a configuration item of an information system and property information of the configuration item, the configuration information management apparatus comprising: a database that stores a configuration item including a set of a property and a value, and knowledge information relating to the set of the property and the value; and a computer to perform the configuration information management including; associating the configuration item with the knowledge information on a basis of the set of the property and the value of the configuration item, and storing the associated configuration item and knowledge information in the database; when a new configuration item is added to the database, determining similarity between the set of the property and the value of the configuration item associated with the knowledge information and a set of a property and a value of the new configuration item; and associating the new configuration item with knowledge information associated with a configuration item having similarity higher than a predetermined threshold on a basis of the determination result obtained by the determining.