An AIS management table 14 is storing entries having, as fields, an input port connected to a section, a section endpoint serving as an input destination, a path over which an AIS frame is to be output, and an output port connected to a section. When a failure is detected in a section, an AIS processing unit 19 searches an AIS management table 14 using, as a key, an input port or section endpoint involved in the location of the failure, inserts retrieved path information into an AIS frame for failure detection, and determines that a retrieved output port is the output destination of the AIS frame. A frame transfer unit 12 receives the AIS frame and information about the output port from the AIS processing unit 19 and transmits the AIS frame from the output port to an adjacent section.