The present invention expands a selective wavelength band and flattens light intensity in the selective wavelength band as good as or better than prior art, and makes power loss less than prior art. The invention as a period characteristic wavelength splitter and an arrayed waveguide diffraction grating wavelength splitter between the first input/output port and the second input/output port in this sequence. The period characteristic wavelength splitter is comprised of the third star coupler, the second arrayed waveguide comprised of multiple waveguides having different optical path lengths, and the fourth star coupler. When an optical signal is input from the first input/output port, the period characteristic wavelength splitter outputs optical signals which wavelengths sequentially deviated with difference .delta. from multiple ports at the first star coupler side of the fourth star coupler. The optical signals which can be output from the multiple ports are all periodic optical signals with waveform difference .DELTA..lambda.for any one of the ports.