Authentication server and authentication method by authentication server

An authentication server capable of determining securely and accurately whether an access source is a cellular phone or a computer when a content is accessed with being limited to cellular phone users. The authentication server including a transmission delay time measuring unit that measures a transmission delay time between the authentication server and a communication terminal over a plurality of times, a transmission delay time distribution property determining unit that determines whether or not a distribution property of the transmission delay time measured over the plurality of times is discrete, and a content access authentication unit recognizing that the communication terminal is a wireless communication terminal and approving the access to the contents when the distribution property of the transmission delay time is determined as being discrete and recognizing that the communication terminal is a wired communication terminal and denying the access to the contents when the distribution property of the transmission delay time is determined as not being discrete.