To omit an operation time of loading a card by providing a portable or a mountable radio transmitter-receiver that sends a radio reply signal including a user ID number upon the receipt of a predetermined radio questionnaire signal.

The user of a public telephone set 2a uses its own arm with a wrist watch 1 mounted thereon on which a radio responder 11 is mounted to hook off a receiver 21. A scanner 22 built in the receiver 21 sends a questionnaire to the radio responder 11 mounted on the wrist watch 1 without direct contact with a public telephone set 2a. The radio responder 11 sends a reply radio wave including an ID number preset for the user. A reader 24a sends an ID number from the radio responder 11 to a center computer 41a via a telephone station exchange 3 to collate the ID number. The center computer 41a sends a line connection instruction to the telephone station exchange 3 when the ID number is collated and coincident with the available telephone number to connect the exchange to a public line.