User equipment used in a mobile communication system is disclosed that includes a specifying unit specifying a tracking area of a serving cell based on broadcast information, a determination unit determining whether the user equipment is entitled to communicate in the private network, and a transmission unit transmitting a signal requesting to update the tracking area to a base station of the serving cell, in which the determination unit determines whether the specified tracking area is for the private network by checking a common identification which is common to private networks, and the determination unit determines whether the user equipment is entitled to communicate in the private network by determining whether the private network to which the serving cell belongs is the same as or different from a private network in which the user equipment is entitled to communicate.