1. A mobile communication system including a mobile terminal (71), a base station (72)
which carries out radio communication with the mobile terminal, and an access management
device (73) which carries out communication with the base station and manages tracking areas,
in which the mobile terminal transmits a tracking area update request signal to the access
management device via the base station,
wherein the access management device is configured to inform the mobile terminal via the base station of a first tracking area update period and a second tracking area period which is different from the first tracking area update period, and
the mobile terminal is configured to carry out a periodic tracking area update using the first tracking area update period or the second tracking area update period.
2. The mobile communication system according to claim 1, wherein the access management device is configured to allocate tracking areas in response to the tracking area update request signal and to transmit a tracking area update accept signal to the mobile terminal via the base station.
3. A mobile terminal (71) used in a mobile communication system including the mobile terminal, a base station (72) which carries out radio communication with the mobile terminal, and an access management device (73) which carries out communication with the base station and manages tracking areas, in which the mobile terminal transmits a tracking area update request signal to the access management device via the base station,
wherein the mobile terminal is configured to carry out a periodic tracking area update using the first tracking area update period or the second tracking area update period informed by the access management device via the base station.
4. An access management device (73) used in a mobile communication system including a
mobile terminal (71), a base station (72) which carries out radio communication with the mobile
terminal, and the access management device which carries out communication with the base
station and manages tracking areas, in which the mobile terminal transmits a tracking area update
request signal to the access management device via the base station,

wherein the access management device is configured to inform the mobile terminal via the base station of a first tracking area update period and a second tracking area period which is different from the first tracking area update period.
5. A base station (72) used in a mobile communication system including a mobile terminal (71), the base station which carries out radio communication with the mobile terminal, and an access management device (73) which carries out communication with the base station and manages tracking areas, in which the mobile terminal transmits a tracking area update request signal to the access management device via the base station,
wherein the base station is configured to inform the mobile terminal of a first tracking area update period and a second tracking area period which is different from the first tracking area update period, transmitted by the access management device.