PURPOSE: To prevent the erroneous connection of a subscriber circuit for TTY by instantaneously cutting the ready read of a terminal equipment from a typewriter when receiving the carrier detection stop information from a modem of a master station and taking a timing from the completion of a data receiving preparation of the modem to a carrier detection.

CONSTITUTION: There is provided a timing circuit 2 for taking the timing of several ten seconds from the transmission of a data set ready signal of a modem to the transmission of a carrier detecting signal of the modem. After a data set ready signal DR is received, when a carrier detecting signal CD does not come on a fixed timing being passed, in the modem, a ready read signal M/D-ER is instantaneously cut. Thereby, even when a general subscriber erroneously receives in a typewriter of a master station, a caller can cut to completely restore the related equipments, so that the typewriter can be controlled with a low cost.