PURPOSE: To allow two people to place a call easiy and surely through a public telephone in the places where they are staying by connecting an inter-telephone set communication control equipment to a public telephone network and further connecting two different telephone sets through said network.

CONSTITUTION: The inter-telephone communication control equipment 6 is connected to the public telephone network 5. The occurrence of communication requests from telephone sets 3 and 4 through the public telephone network 5 is detected, and passwords transmitted from the telephone sets 3 and 4 are temporarily accumulated. When the passwords are transmitted from the telephone sets 3 and 4 that request communications, the accumulated passwords are retrieved, and if the same passwords lie, the telephone sets 3 and 4 with the same passwords are connected. Consequently that system has such advantages that both communication sides are callers and that no identification of telephone numbers(hardware) through that of callers(the identification of key numbers and software) is needed. Thus two parties in the places where they are staying right now can communicate with each other on the phone easily and inexpensively.