PROBLEM TO BE SOLVED: To provide: a waveguide optical wavelength filter capable of making inter-polarization conversion of a TM wave component and TE wave component; and a combiner/splitter produced using the same.SOLUTION: An optical wavelength filter comprises a first optical wavelength filter 11a, a second optical wavelength filter 11b, a polarized wave branching filter 21, and a wavelength splitter 22; one end of the first optical wavelength filter 11a being connected to a third input/output port 21c of the polarized wave branching filter 21, one end of the second optical wavelength filter 11b being connected to a fourth input/output port 21d of the polarized wave branching filter 21, and a third input/output port 22c of the wavelength splitter 22 being connected to a first input/output port 21a of the polarized wave branching filter 21. One end of a basic propagation mode waveguide is connected to a second input/output port 21b of the polarized wave branching filter 21 and the other end thereof is connec