When a document in which a shortcut has been set is exchanged to another document, a shortcut to the document before the exchange is enabled to effectively act on the document after the exchange. When a formation of a shortcut of the document is instructed, the shortcut including a document ID of the document is formed and attributes (shortcut formation history) of the document are updated. After that, when a deletion of the document into a trash box and a formation of a proxy entity of the document are instructed, a proxy entity in which a user ID set into the document to be deleted has been set is formed. The proxy entity is formed in a same folder as a folder in which the deletion document exists. The document ID of the deletion document and the document ID of the formed proxy entity are exchanged and the deletion document is moved into the trash box.