A relationship-information storage unit stores relationships between configuration items. The configuration items belong to an information system and are stored in multiple databases. A first counting unit compares, across the databases, attribute values of one configuration item in each of the databases, thereby counting a matching-attribute-value count. A second counting unit identifies a configuration item having a relationship with the one configuration item, for which the first counting unit counts the matching-attribute-value count, by referring to the relationship-information storage unit. Then, the second counting unit compares, across the databases, attribute values of the identified configuration items to count a matching-attribute-value count. A similarity calculation unit calculates similarity between the configuration items, based on the matching-attribute-value count counted by the first counting unit and the matching-attribute-value count counted by the second counting unit.