An internet adapter connected with a conventional telephone has a problem that it cannot switch the connection, when the internet telephone cannot be utilized, to the public line and therefore it cannot make a call as an ordinary telephone. In a talking device adapter connecting the public line and an IP network, a public line signal transceiver unit (1100) inputs speech information and the telephone number through a telephone (10), and a destination identifying unit (200) acquires an IP address corresponding to the telephone number to generate path selection information and transfer it to a line connection switching unit (100). In accordance with the path selection information, the line connection switching unit (100) selects either the path of a public line (13) or a path from an IP network communication processing unit (5000) through an IP network (14), and transmits the speech information to a telephone (20).