A mobile radio terminal includes a radio transmission/reception unit and a control unit. The radio transmission/reception unit uses a radio signal to perform transmission and reception to and from a base station belonging to a circuit switching network, and also uses a radio signal to perform transmission and reception to and from a base station belonging to a mobile communication network. The mobile communication network is connected to the circuit switching network and forms an integrated communication network together with the circuit switching network. When the mobile radio terminal is on standby in a base station belonging to the mobile communication network, the control unit activates the radio transmission/reception unit and controls the radio transmission/reception unit so as to maintain synchronization with a base station belonging to the circuit switching network.