PURPOSE: To transmit control information with a PB signal from a DP subscriber by controlling automatically the transmission time of the DP/PB signal.

CONSTITUTION: When a handset 1 is hooked off, a handset state detecting part 2 detects this state and reports it to a DP/PB signal determining part 3 through a report line 4. The determining part 3 reports it to a DP/PB signal generating part 7 through a report line 9 that DP signal transmission is determined. The determining part 3 monitors intervals of instruction dialing of a user; and if intervals are shorter than a prescribed time, the generating part 7 continues to output dial information to a telephone line 10 with the DP signal because determination of DP signal transmission is not changed. If said intervals exceed a certain time, determination of PB signal transmission is reported to the generating part 7.