An X-ray apparatus is disclosed which includes a mirror having a reflection surface, for expanding an X-ray beam in a predetermined direction, a detecting device for detecting a relative positional relationship between the X-ray beam and the reflection surface with respect to a direction perpendicular to the reflection surface, and an adjusting device for adjusting the relative position of the X-ray beam and the reflection surface on the basis of the detection. Also disclosed is an exposure apparatus and a semiconductor device manufacturing method using the Xray apparatus.