In a mobile communication system for authenticating a communicating party when communication is performed between a mobile terminal and a device on the side of a network, the mobile terminal, upon receiving a request signal requesting operation execution from the network device, sends the network device an authentication request signal in order to determine whether the request signal is a request signal from an authorized network device, and performs an authentication operation. The network device executes an authentication operation based upon the authentication request signal received from the mobile terminal and sends a result of the authentication operation to the mobile terminal. The mobile terminal compares the result of its own authentication operation and the result of the authentication operation sent from the network device and executes an operation that is in accordance with the request signal only if authentication that the network device is an authorized network device is obtained based upon agreement of results.