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. A first base station communicates with a mobile communication terminal by using a first frequency, and a second base station communicates with the mobile communication terminal by using a second frequency. And while the mobile communication terminal is communicating with the first base station by using a channel, the reception quality of the second frequency is measured corresponding to the change of the quality of the channel, and the channel is changed over to the second base station corresponding to the measured reception quality and the change of the quality of the channel. And in case that the quality of the channel is within a predetermined first range and when the change of the quality of the channel is larger than a designated value, the reception quality of the second frequency is measured at the mobile communication terminal. And in case that the quality of the channel is without the predetermined first range, the reception quality of the second frequency is measured more frequently at the mobile communication terminal, compared with the case that the quality of the channel is within the predetermined first range.