MOBILE COMMUNICATION SYSTEM, MOBILE STATION USED FOR THE SAME, AND EXCHANGE

PROBLEM TO BE SOLVED: To provide a technology for restraining a large number of mobile stations from registering their positions simultaneously, without having to provide a relay device. SOLUTION: A mobile communication system is equipped with a random timer, which controls the start timing of a position registration request; a storage mean which stores a position code which indicates a current position registration area, control channel frequencies in a radio zone in the vicinity, and identification data(ID) of turning the random timer on or off; a comparison means, which compares a position code which indicates a new position registration area, when a mobile station moves out of a present position registration area with the position code that indicates the stored position registration area; another comparison means which compares a control channel frequency in a new radio zone with that in the stored radio zone; and a discriminating means which discriminates the content of the stored identification data. In a case the position codes are different from each other, the control channel frequencies match each other, and the identification data indicates that the random timer is turned on, the random timer is turned on, and a position registration request is made using its time-out as a trigger.