Base stations of a communication system belong to a sub-network, which is connected to the Internet by way of a gateway. Base stations of another communication system belong to sub-network, which is connected to the Internet by way of another gateway. A mobile terminal communicates with a server by using one of the communication systems. In this case, the mobile terminal includes mobile station network interfaces which can access to the communication systems, and is designed to switch communication systems by means of a communication system switching unit.