To simplify signal lines among packages of a monitor section by using an idle cell in the equipment so as to multiplex various alarms and state signals in the equipment onto the idle cell and to transmit the resulting cell.

The equipment detects idle cells in main signals 101, 105, 109, 113 and multiplexes various alarms and state signals 104, 108, 112, 116 onto idle cells by each package, detects the result at a final package and sends the package to monitor sections 11, 21, 31, 41. Each package has an idle cell detection circuit 12(22, 32, 42) and various alarm and state signal multiplexer circuit 13 (23, 33, 43).