PURPOSE: To decrease the give-up of a call on the way of calling of a caller by using a detected output of a ring tone detection circuit so as to start dialing a transfer destination telephone number from a selection signal generator.

CONSTITUTION: When the handset of a transfer destination telephone set is picked up, the polarity of a calling line R2 is inverted. The inversion is detected by a polarity inversion detection circuit 4 and fed to a control circuit 21. As a result, relays Rl1, Rl2 are excited, an incoming line R1 and the line R2 are connected via relay contacts rl1, rl4, rl3 and the talking by transfer is attained. When the talking is finished and the handset of transfer destination is hooked on the telephone set, the polarity of the line R2 is inverted again and the level of a trunk line L1 of the line R2 is inverted from negative into positive level and that of the trunk line L2 is inverted from positive to negative level. The inversion is detected by the circuit 4, the output is transmitted to the circuit 21, which controls relays Rl1, Rl2, Rl4 and Rl5 into the inactivated state, the relay contacts are brought into the state as shown in Fig. and the incoming of the next level signal is awaited.