A communication server communicates with a radio base station that is capable of being connected to a fixed line by a user. A receiving unit receives station identification information identifying the radio base station and line identification information identifying a fixed line to which the radio base station is connected. An acquiring unit acquires authentication information indicating preliminarily set correlations between the station identification information and the line identification information. A determining unit determines whether a correlation between the station identification information and the line identification information received by the receiving unit coincides with a correlation indicated in the authentication information acquired by the acquiring unit. A determination result output unit outputs a determination result of the determining unit.