PURPOSE: To improve the workability for the setting or change of an identification number and to obtain the identification number from a called equipment number by handling a dial number on digit-by-digit basis and combining numbers of respective digits and outputs of multiplying circuits into the identification number.

CONSTITUTION: The paging system consists of a calling device 2, a transmitter 3 and an antenna 4, and an identification number difference reporting device 5. The identification number extraction part of this calling device 2 consists of a number development circuit 72 and a number converting circuit 73; called number information received by the circuit 72 is outputted, digit by digit, from the 1st∼the 4th number development circuits 721∼724 and a 4-digit decimal number is outputted from the circuit 72. The output of this circuit 72 is applied to the converting circuit 73 consisting of an identification number switching circuit 731, plural doubling circuits 732 and an adding circuit 733. Then, the input to the adding circuit 733 is allowed to include 1-digit numbers of every digits or one multiplied 1-digit number of the circuit 732, thus improving the workability for the setting or change of the identification number.