Patent ID: 8731173

Claim:
A telephone exchange system, comprising: a connection interface connecting a communication line with a plurality of extension telephones; a database including: a dial-in conversion table registering a received number of a dial-in incoming call from the communication line in association with a number after conversion of the received number; and an extension number table registering an extension telephone of the plurality of extension telephones in association with an extension number of the extension telephone; and a main controller, comprising a processor, connected to the connection interface and the database, wherein the main controller sets in advance whether, when the dial-in incoming call comes, the dial-in conversion table is used or the extension number table is used and, in a case where the use of the extension number table is set in advance, retrieves the extension number coinciding with the received number from the extension number table when the dial-in incoming call comes, and causes the extension telephone corresponding to the extension number to ring when there is the extension number coinciding with the received number.