PURPOSE: To use a bypass line to public networks and a line changeover controller efficiently by connecting one changeover circuit to the plural public networks with different call drive methods and connection procedures so as to use them on purpose.

CONSTITUTION: Drive circuits 16,17 have functions in matching with the connecting condition and the drive procedure of a public network to be driven and a storage circuit 18 stores a public network being a bypass destination, its call drive method and connection destination with respect to a private line requesting changeover. A control circuit 19 regards a private line 31 as a fault when interruption of a carrier received from a detection circuit 12 is consecutive for a prescribed time or over, reads a public network being a bypass destination with respect to the line 31, its call drive method and connection destination and gives a command to a line circuit 14 to make dialing to the public network being the bypass destination through the use of an idle public line 41. The line circuit 14 makes dialing by the circuit 16 according to the command and it is informed to the circuit 19 after the connection. The circuit 19 gives a command of the changeover from the line 31 regarded to be a fault by the circuit 14 to the changeover circuit 11 and recovery is informed from the circuit 12 to the circuit 19 from the interrupt of a carrier of the line 31.