Abstract: In a system for use in opening a destination terminal from an information processing unit through a communication control unit and a public telephone network, a primary opening command is delivered only once in response to an opening request from the information processing unit to the communication control unit, with the primary opening command accompanied by a dial number and a terminal identifier assigned to the destination terminal. The communication control unit at first forms a communication path by the use of the dial number included in the primary opening command and thereafter transmits to the destination terminal, as a secondary opening command, a part of the primary opening command from which the dial number has been removed. The destination terminal is opened in response to the secondary opening command under the control of the communication control unit.