A cellular phone system, in which the probability that the deterioration of channel quality and the phenomenon of a call drop occur caused by the imperfection of the control of the changing over to the different frequency can be lowered and the channel quality can be made to be higher, is provided. The method also includes maintaining the network connection by monitoring the connection and, upon determining that the connection has been lost, selecting a another available network for use and connecting the wireless device the other network. Subsequently, the NMOS 62 becomes on-state and decreases the driving voltage Vi of the node N6.