PURPOSE: To exactly adjust the position and figure of a mirror by making use of visible light in a synchrotron radiation light and observing the positioning mark drawn on an X-ray mirror.

CONSTITUTION: On the first end surface S1 of a base plate 13a for an X-ray mirror coated on the surface with metal film 13b, a pair of first positioning mark M1 is drawn, and also on the second end surface S2, a pair of second positioning mark M2 is drawn. This mirror 13 is arranged in the light path of synchrotron radiation light 11 in a beam line 12. With the aid of the visible light in the radiation light 11, a projection image M3 of a pair of marks M1 projected on the second end surface S2 and a pair of marks M2 are observed simultaneously with an observation means 20 and the figure of the mirror 13 is adjusted. By this, the image M3 and the mark M2 coinsides on the end surface S2 and also, the line connecting between the image M3 and the mark M2 is adjusted horizontal.