Stage orthogonal error and position errors caused by mirror distortion are reduced. A CPU calculates a coordinate error (Δx,Δy) between a measured XY coordinate (x,y) of each of arbitrary reference points on a wafer W0 loaded on a XY stage which is measured by a laser interferometer and a calculated ideal position XY coordinate of the reference point, calculates an orthogonal error of the XY coordinates on the bases of the calculated coordinate errors (Δx,Δy) and an error due to mirror distortion, and stores them in a storage device. When a wafer W is actually inspected, the CPU corrects the measured position coordinates (x,y) from the laser interferometer on the basis of the calculated orthogonal error, and corrects beam deflector for deflection on the basis of the calculated error due to mirror distortion.