In a portable telephone system, in order to constantly ensure an optimum communication environment for wireless communication terminal that continues communication while its position is moved, a process for switching a base station (hereinafter, referred to as a handoff) to be connected is performed depending on a radio wave condition with the wireless communication terminal.
The wireless communication terminal measures both strength of a signal transmitted from the base station under communication and strength of a signal transmitted from other peripheral base stations other than that base station to carry out a process for maintaining more suitable radio state.
For instance, in the case of a CDMA portable telephone of an IS95 system (CDMA2000 1x system), the portable telephone measures a signal strength from a base station with which the portable telephone currently communicates and a signal strength from peripheral base stations other than that base station.
Then, the portable telephone informs the base station of the measured signal strength while the portable telephone is under communication, and entrusts the base station to determine the handoff.
Further, during the idle state of the portable telephone, the terminal itself determines to switch the base station based on the measured result (for instance, see Patent Document 1).    Patent Document 1: JP-A-2002-171555