For use in combining and/or splitting a 3-wavelength multiplexed light, in which if central wavelengths of the three bands are denoted as .lamda.1, .lamda.2 and .lamda.3, in a relation that 0.92.ltoreq..lamda.2/.lamda.1.ltoreq.1.08, 0.20.ltoreq..lamda.3/.lamda.1.ltoreq.0.92 or 1.08.ltoreq..lamda.3/.lamda.1.ltoreq.5.00, the wavelength multiplexing and demultiplexing device comprises two optical filters of different characteristics, supported by one of more optical substrates combined in a single package, wherein, when a 3-wavelength multiplexed light is led to a first filter A for splitting the 3-wavelength multiplexed light into light of a band of .lamda.3 and a 2-wavelength multiplexed light of .lamda.1 and .lamda.2, and when the 2-wavelength multiplexed light is led to a second filter B for splitting the 2-wavelength multiplexed light into light of a band of .lamda.1 and light of a band of .lamda.2, an optical edge filter is used for the filter A and an optical band-pass filter is used for the filter B.