A X-ray waveguide includes a core for guiding X-rays having a wavelength band in which the real part of refractive index of material is smaller than 1 and a cladding for confining the X-rays in the core. The core has a one-dimensional periodic structure in which a plurality of layers respectively formed of inorganic materials having different real parts of refractive index are periodically laminated. The core and the cladding are configured so that a critical angle for total reflection for the X-rays at an interface between the core and the cladding is larger than a Bragg angle due to a periodicity of the one-dimensional periodic structure. A critical angle for total reflection for the X-rays at an interface between layers in the one-dimensional periodic structure is smaller than the Bragg angle due to the periodicity of the one-dimensional periodic structure.