An optical network system is disclosed by which flexible wavelength path setting can be performed in accordance with tree-shaped and star-shaped network topology. A central node (2) includes a multiplexing section (2a) for multiplexing optical signals transmitted from user nodes (3-1 to 3-k) and inputted thereto, and a central node side branching section (2b) for branching the optical signal multiplexed by the multiplexing section (2a) and supplying the branched optical signals to the user nodes (3-1 to 3-k). Each of the user nodes (3-1 to 3-k) includes a transmission section (3f) capable of outputting an optical signal to which transmission wavelengths different from those of the other user nodes are set, and a reception section (3p) for extracting selected optical wavelength components from the branched light supplied thereto from the central node side branching section (2b) and extracting optical signals from the extracted optical wavelength components.