The objective of the present invention is to easily acquire necessary information at arbitrary times. According to this invention, folder names that indicate directories are correlated with IDs, and are hierarchically managed in accordance with the correlated IDs; upon receiving an access email from a cellular phone, the folder names correlated with the IDs are examined, and a reply email that includes a folder name included in a first rank and a folder name included in a second rank immediately below the folder name is generated; the reply email is transmitted to the cellular phone at an accessing source; upon receiving an access email from the cellular phone, it is determined whether the email includes the folder name in the second rank that is included in the reply email; when it is determined that the email includes the folder name, the folder names correlated with the IDs are examined, and a reply email that includes a folder name in the second rank and a folder name in a third rank immediately below the folder name is generated; and the reply email is transmitted to the cellular phone at the access source.