Abstract: An improvement is made in an intelligent modem system which can operate selectively either in a transparent mode in which a modem circuit of the system is placed in a data communication relationship with an information processing terminal while the modem circuit is connected with a public communication line, or in an escape mode in which the modem circuit of the system is placed out of the data communication relationship from the information processing terminal to permit altering of the status of the modem circuit while the modem circuit is connected with a public communication line, by using a switch element for selectively placing the modem circuit of the system in a data communication relationship, with the information processing terminal, when a manual reception and/or transmission mode is selected, also for effecting a change-over between the transparent mode and the escape mode, when an automatic reception and/or transmission mode is selected.