To surely and also quickly construct a radio communication channel when a cable communication line is disconnected by intermittently sending a calling signal to a general telephone, constructing an analog signal path in other timings, converting an analog signal of the general telephone into a digital signal to transmit to a radio telephone and on the other hand, transmitting an analog signal from the radio telephone to a feeder circuit.

A communication connection circuit EQU mediates signal exchanges between two kinds telephones, i.e., a portable telephone 1 and a telephone set 2 based on the operation of a control circuit 3. A calling circuit 4 generates 16Hz calling tone under the control of the controlling part 3. A feeder circuit 6 intermittently sends a calling tone to the telephone set 2 under the control of the circuit 3, and on the other hand, feeds direct current voltage to the telephone set 2 in the other timings and constructs an analog signal path. A DTMF detection circuit 5 converts dial information that is outputted by the set 2 into a digital signal and transmits it to the circuit 3. A hybrid circuit 7 transmits a signal of the telephone 2 to the circuit 6.