The present invention provides a polarized light mode converter which can be provided within a two-dimensional photonic crystal or can be smoothly connected to a two-dimensional photonic crystal. In a two-dimensional photonic crystal made of a slab-like main body provided with a plurality of different refractive index regions (for example, holes 22) arranged in a lattice in the main body, where the different refractive index regions have a refractive index different from that of the main body, a polarized light conversion waveguide 23 is formed which is comprised of defects of the different refractive index regions arranged linearly whose a cross-sectional shape is asymmetrical in a vertical and in a horizontal direction. The polarized light conversion waveguide 23 can be, for example, realized by providing, on a side of the waveguide, holes 221 and 222 extending in a direction oblique to a the main body surface. TE polarized light propagating through the polarized light conversion waveguide 23 is partially converted into TM polarized light due to the asymmetry of the cross-sectional shape of the waveguide. Since the polarized light mode converter is made of a two-dimensional photonic crystal, it can be provided within a two-dimensional photonic crystal or can be smoothly connected to a two-dimensional photonic crystal.