A communication system includes: a base station device that performs wireless communication with a mobile terminal; a gateway device that is connected to the base station device and provides the mobile terminal via the base station device with a connection path to a network; an authentication server that is connected to the gateway device and issues an authentication key to the mobile terminal via the gateway device and the base station device; and a position search server which outputs a request requesting determination of position of the mobile terminal, wherein, the authentication server identifies the authentication unit from the first registration table, and outputs the request to the identified authentication unit, the authentication unit identifies the data path unit or paging controller unit from the second registration table, and the position search server obtains position information of the mobile terminal from the identified data path unit or paging controller unit.