PURPOSE: To extend the configuration into 1:N redundant configuration while keeping in-service in matching with increase in channel demand without causing cost increase regardless of an equipment of 141 redundant configuration at the introduction of an initial stage.

CONSTITUTION: Selectors 51, 52 for 141 redundant configuration and 1:N selectors 53, 54 for 1:N redundant configuration are arranged to a switch circuit 5. The 1:N selector 53 provides an output of the output from the selector 51 or an input signal from a terminal 55 of a 1:N interface 59 to a terminal 57 of the 1:N interface 59. The 1:N selector 54 selects a signal from an optical interface 3 or an input signal from a terminal 58 of the 1:N interface 59 and outputs the selected signal to a standby system circuit of a low-order group signal interface circuit 6. An input signal from the terminal 58 of the 1:N interface 59 is outputted to a terminal 56 of the 1:N interface 59.