To unequivocally establish synchronization at the receiver end, to prevent degradation of reception quality and to transmit mixed signals of different bit rates.

An output control unit 102 outputs data of a bit rate A to a header attaching unit 104 and outputs data of a bit rate B to a header attaching unit 105. A bit rate instructing unit 103 instructs the header attaching unit 104 or the header attaching unit 105 to attach a header of the bit rate A being the least bit rate. The header attaching unit 104 creates a header of the bit rate A, including an ID of a destination ONU 300 of the data and the data length, and attaches it to the data of the bit rate A. The header attaching unit 105 creates a header of the bit rate A, including an ID of the destination ONU 300 of the data and the data length, and attaches it to the data of the bit rate B.