PURPOSE: To efficiently use communication channels by practically reducing a radio zone of high use rate and securing an idle channel for a new call in this zone in the mobile communication system where a mobile machine measures the field intensity of the control channel of a base station to find a base station at the movement destination.

CONSTITUTION: A hand-over switching reference level transmitting means 15 in a control station 11 monitors the use rates, namely, the traffic of communication channels in reference stations 131 to 13n in a control zone and discriminates the hand-over switching reference level in each of new radio zones 121 to 12n based on this monitor information and transmits the hand-over switching reference level higher than the present value to the reference station in the radio zone where the use rate of communication channels is higher. Thus, hand-over is requested to a mobile machine placed in the periphery of the radio zone, where the use rate of communication channels is high, out of plural radio machines placed in this radio zone through its hand-over means, and an idle channel is secured even in the zone of high use rate.