Abstract: An interface device for transmitting data for data communication in an analog exclusive line includes a modem unit for modulating data, an impedance matching unit for matching an impedance with the analog exclusive line, an FXS signal unit for recognizing a connection request signal from an FXO interface, a hybrid 2:4 wire conversion unit for converting a four wire interface from the modem unit into a two wire interface for the analog exclusive line, and a main processor. The FXS signal unit uses the analog exclusive line which does not have an exchange, and thus performs the data communication as in the PSTN. The modem unit is informed of the connection request signal from another device by a local ring generating unit.