An apparatus for X-ray analysis includes (1) a focusing optical system including an X-ray source, a specimen table and a two-dimensional X-ray detector, (2) a device for shifting the angle of incidence of X-rays relative to a specimen supported by the specimen table, (3) a device for moving the two-dimensional X-ray detector in parallel with a central axis of rotation of the specimen and (4) a mask arranged in front of the two-dimensional X-ray detector. The mask has a slit arranged on a line intersecting a plane rectangularly intersecting the central axis of rotation of the specimen and containing a central optical axis of incident X-rays. The mask is driven to move in parallel with the axis of rotation of the specimen so that measuring can be conducted.