PURPOSE: To perform radio communication by using an existing radio telephone set as it is, by using an adaptor provided with a radio transmission/reception means radio-connected to a connection master device, a telephone set control means, a DC power supplying means, etc.

CONSTITUTION: When a wire telephone set is connected to the connection mechanism B1 of a radio telephone adaptor B which incorporates the DC power supplying means B2, a call emitting signal and a dial signal from the wire telephone set are detected at the telephone set control means B4, and are radio- transmitted via the radio transmission/reception means B3, then, are received at the connection master device A. And a line is connected to a corresponding wire telephone line via the device A. The connection to the wire telephone set via the wire telephone line is performed similarly, thereby, it is possible to perform the radio communication easily and surely without using the radio telephone set by using the existing wire telephone set as it is.