A customer premises optical network unit (ONU) comprises: an electrical/optical transform unit 6 to be connected with an optical transmission path 2 at a central office side for performing an opto-electrical transform and an inverse opto-electrical transform; an ONU function part 7 to be connected with an electric signal input and output terminal of the electrical/optical transform unit 6; a serial/parallel transform unit 8 to be connected with a parallel signal terminal of the ONU function part 7 for performing a serial/parallel transform and an inverse serial/parallel transform; and a multi source agreement interface module 9 to be connected with a serial signal terminal of the serial/parallel transform unit 8.