When a retrieval condition including a first desired word and a first desired component including a value in which the first desired word is included, is inputted, a first detecting device detects second desired components each being similar to the first desired component, an acquiring device acquirers second desired words each being similar to the first desired word, a first retrieving device retrieves first structured documents each including a first component including a value in which one of the first desired word and the second desired words is included, a second retrieving device retrieves second structured documents each including a second component corresponding to one of the first desired component and the second desired components and including or corresponding to the first component.