In the present invention, as a mobile communication terminal, which is using service in the area of an asynchronous mobile communication system, detects signals from a synchronous mobile communication system, the mobile communication terminal repeatedly performs a process of examining whether, in a predetermined time, signals from the asynchronous mobile communication system have been detected a designated number of times, and measuring the intensity of the signals. When the number of times that the intensity of signals from the asynchronous mobile communication system is smaller than a designated number of times, or no signals from the asynchronous mobile communication system are detected, within the predetermined time, it is determined whether to perform handover of the mobile communication terminal.