Mobile communication system and location registration method in mobile communication system

A mobile station, operable in a mobil communication system that executes a location registration processing by using the channel quality of a base station and an information concerning a base station the mobile station includes a base station information memory unit for storing therein information concerning a plurality of base stations and an amount in which the channel quality of the base station is changed with time and a location judging unit for judging on the basis of the amount in which the base station information is changed with time and which is stored in the base station information memory unit whether or not location registration processing is to be executed indicating a location in service area. Whether the location registration processing is to be executed or not is determined in accordance with the moving speed of the mobile station, thereby limiting the occurrence of a location registration request which becomes invalid with a large possibility in a short period of time because the mobile station moves to another location registration area or to the calling area in a short period of time.