A mobile communication system is provided such that multiple identity codes assigned to a terminal device are displayed on the terminal device, whereby such multiple identity codes are selectively and arbitrarily used without a specific provision, and an identity code is displayed according to an arrival of an appropriate notification chance. A subscriber identity code notification apparatus is also provided. A subscriber identity code holding device holds multiple identity codes such as telephone numbers, which are applicable to a single terminal device and which are different depending on the telecommunications carrier. A subscriber identity code notification apparatus is provide such that the subscriber identity code held by the subscriber identity code holding device notifies the terminal device of the corresponding subscriber identity code, in discrimination of an arrival of a given notification chance.