PROBLEM TO BE SOLVED: To provide such a discrimination method for the diameter of a mask that can eliminate a measuring error in an X-ray analysis without requiring a special apparatus and increasing the number of elements to be measured, and that can discriminate the diameter of the mask in a short time. SOLUTION: A sample stage 19 which supports sample 1 is moved in the radial direction of a mask 3. In parallel with this operation, scattered rays by one kind or a plurality of kinds of fluorescent X-rays B2 which are generated from a part on the mask 3 or by primary X-rays B1 which are reflected by the mask 3 are detected through a diaphragm hole 14A for visual-field restriction. The intensity of the detected X-rays is compared with a reference intensity, and the diameter of a mask hole 4 is discriminated.
