PURPOSE: To convert the positions and speeds of overhead bytes under constant conditions by changing a selection of control signal data with a 2nd address of the output of a storage part and varying the positions of the multiplexing of plural overhead bytes.

CONSTITUTION: A counting part 120 inputs and counts a clock in order by a specific number and outputs a 1st address, which is inputted to the storage part 160, so that the 2nd preset address corresponding to the 1st address is read out and outputted. Then a control part 140 selects and outputs one of (m) input control signal data with the 2nd address outputted by the storage part 160. In this case, the selection of control signal data with the 2nd address outputted by the storage part 160 is changed. Consequently, the positions of the multiplexing of plural overhead bytes can be shifted mutually and various customer's requests can be handled.