When a call is received at the TAD from telephone 1 via exchange A2 and exchange B3, the TAD transmits an outgoing message. In response to the aforementioned message, the caller transmits a message or telephone number data regarding his own telephone. After the TAD records the telephone number, it calls up portable telephone 6 by autodialing. When TAD and portable telephone 6 are in a connected condition via base station 5, and if TAD sends the telephone number data in a predetermined format, it will be displayed upon the display unit of portable telephone 6.