Abstract: An X-ray mirror apparatus includes a substantially cylindrical mirror body and a pair of light shielding members provided at both open ends of the mirror body. The inner surface of the mirror body constitutes a reflecting mirror surface having a surface of revolution. Each light shielding member has a light shielding plate arranged at the opened end of the mirror body to block it, and an annular slit allowing passage of X-rays entering onto and reflected on the reflecting mirror surface. A cylindrical fitting member is fixed to the light shielding plate to be coaxial with the slit. The fitting member is fitted on the opened end portion of the mirror body, thereby positioning the light shielding member so that the slit is located coaxial with the axis of the reflecting mirror surface.