PURPOSE: To measure the shift, from the direction perpendicular to the reference surface, of the axis of a charged-particle beam simply and accurately by providing plural marks located at proper intervals on the same member, and carrying out detections by making the positions of the marks relative to the direction perpendicular to the reference surface different.

CONSTITUTION: Reference plates 1X and 1Y are fixed to a stage 2 in such a manner that they can be rotated either manually or with different motors driven by the commands of a cpu5. At first, marks (M1) and (M2) are detected after the reference plate 1X(1Y) is inclined at an angle (θ) clockwise from the reference surface. Next, the marks (M1) and (M2) are detected after the reference plate 1X (1Y) is inclined at an angle (θ) in the reverse direction from the original state [counterclockwise from the direction (Q) which is perpendicular to the reference surface]. As the result of such detections, the outputs of Lcosθ+E1 and Lcosθ- E1 are sent from a computing circuit 12 to the cpu5. After that, the cpu5 divides the value 2E (=2Lsinθ tanθ) which is the difference between the above two measurements by two (so as to obtain the average), and computes the shift of the beam axis to the direction (Q) which is perpendicular to the reference surface.