PURPOSE: To judge the necessity of extension of base stations by informing position registering information related to in/out time of a slave equipment to/from a zone from a base station to a control device through an exchange and allowing the control device to measure traffic based upon the position registering information.

CONSTITUTION: A slave equipment 40 moving among plural zones radiates a radio wave indicating the existence of its own station at intervals of a fixed time and a position regitering information informing part 21 in a base station 20 recognizes in/out of slave equipments 40 in its own zone and stores position registering information consisting of a zone identifier(ID), a slave equipment ID, moving time, etc., in a storage part 31 consisting of a ROM, a disk, or the like. A control part 32 generates roaming history information in each slave equipment by collecting the position registering information and tabulates the idle/busy time data of a line, the history information of incoming success/failure calls, etc., in each zone to measure traffic. The traffic is measured in each week e.g. and when the index of a line using rate exceeds a reference value, necessity of extending the line is judged.