To establish a method for generating an X-ray microbeam which keeps the degree of asymmetry and the condensing factor at a constant value even if the wavelength of X rays changes by changing angles of incidence and outgoing to the surface of a crystal with the Bragg condition maintained by rotating the crystal around an axis perpendicular to the surface of a reflecting grating.

An asymmetrical factor due to the fluctuation in the energy of X rays is maintained constant to make it possible to scan the energy of incident X rays without changing condensing efficiency. If is also possible to keep the degree of asymmetry at a constant value even if the wavelength of selected X rays changes. Furthermore, a condensing condition including the energy and beam size of X rays can be set independently. Therefore, such difficulties as the change in the degree of asymmetry and condensing efficiency can be solved. An asymmetrical factor due to the charge of the energy of X rays can be maintained uniformly and it is made possible to scan the energy of incident X rays without changing condensing efficiency by varying angles of incidence and outgoing to the surface of a crystal without disturbing the Bragg condition through the rotation of the crystal.