There is provided a filter assembly for combining a wavelength multiplexed optical signal by multiplexing optical signals of different wavelength emitted from respective optical devices, and/or for dividing a wavelength multiplexed optical signal into optical signals of different wavelength and causing the optical signals of different wavelength to enter respective optical devices. This filter assembly comprises: a light transmitting member within which each optical signal propagates; plural optical filters disposed on an upper face of the light transmitting member at a predetermined spacing wherein each optical signal passes through the optical filters; upper reflective layers respectively provided between adjacent ones of the optical filters; and a lower reflective layer provided on a lower face of the light transmitting member, and wherein the wavelength multiplexed optical signal propagates along the same optical path within the light transmitting member.