To provide an x-ray filter capable of suppressing reduction in the intensity of filtered x-rays and capable of reducing x-rays with energy higher and lower than the energy of a target x-ray.

The x-ray filter composed of a periodical structure film divides an x-ray made incident on the periodical structure film at a fixed angle into an energy region A reflected by total reflection of the periodical structure film, an energy region B reflected by Bragg reflection corresponding to the structure period of the periodical structure film and a transmission energy region located between the energy region A and the energy region B to transmit the x-ray. The x-ray filter selects and obtains an x-ray transmitted through the transmission energy region out of incident x-rays.