RADIO TERMINAL DEVICE

Provided are a wireless access protocol and a portable terminal device which can prevent the generation of inconsistencies in Idle-mode Signaling Reduction (ISR) states within a network. As a result of ISR being enabled between a portable terminal device (1) and a network (2) which are capable of communicating by using the communication protocols of a plurality of wireless access technologies, the portable terminal device (1) performs position registration processing between the plurality of wireless access technologies and the portable terminal device (1) each time a fixed period of time elapses, and the portable terminal device (1) is able to move between the plurality of wireless access technologies that have already been registered, without conducting new position registration processing. At this time, if there is a possibility of there being a difference in ISR states (activated or not activated) between the portable terminal device (1) and the network (2), the portable terminal device (1) ignores any instructions issued by the network (2) for ISR to be enabled in the portable terminal device (1).