PURPOSE: To attain again a communication with a holding subscriber by the operation of a held subscriber by detecting dial number information of the subscriber to be held in holding state so as to call the held subscriber.

CONSTITUTION: After extension telephone sets A and B make a communication via an extension mutual trunk IOT0, the extension telephone set A holds the telephone set B and when the extension telephone sets A and C make a communication via an extension mutual trunk IOT1 and the holding extension telephone set B desires quickly a communication with the A again, the telephone set B is hooked off and connected to the outgoing register ORT. A central controlller discriminates that the telephone set B is subscriber to be held, the holding information and the allocated location information to be held of the telephone set A are transmitted to the register ORT. Then, when the telephone set B dials a holding call number, the information is analyzed by a hold access trun, transmitted to the central controller, which controls the telephone set A to transmit a holding call tone, and the communication with the telephone set B is attained by the response to the telephone set A.