There is provided a mirror supporting structure for a monochromator capable of turning the mirrors about axis lines which cross each other, thereby adjusting the attachment angles of the mirrors in two directions. The mirror supporting structure for a monochromator comprises first angle adjusting means for turning the mirrors about each first axis line which does not cross each plane direction of the mirrors and second angle adjusting means for turning the mirrors about each second axis line which does not cross each plane direction of the mirrors at right angles but is parallel with a line crossing the first axis line. The first angle adjusting means comprises a first leg member and a second leg member which are disposed to be spaced from each other, and a support member installed between the first leg member and the second leg member and supporting the mirrors, and wherein the mirrors are supported by the support member in a manner that each plane direction of the mirrors does not cross the installing direction of the support member at right angles, and the support member can be turned about a line which is parallel with the installing direction of the support member.