PURPOSE: To examine the irregularities of a sample surface by detecting the focusing at a plurality of points on the sample surface, storing a focal distance of each surface point, subjecting it to interpolation calculation, and scanning the sample surface while making focus adjustment.

CONSTITUTION: A sample is set and a program in which a plurality of focus confirmation points are designated is stored in a control device 8. The control device 8 reads the output of a secondary electron detector 6 per scanning operation to perform data processing by radiating an electron beam, and scanning along a single X-ray passing a focus confirmation point while changing the focal distance of an objective lens 3 with respect to each focus confirmation point. The focal distance of the objective lens 3 having a largest amount of high frequency components is searched from among the video signals and is made a focal distance data of the focus confirmation point and is stored in a memory 9. Subsequently, the actual operation is performed. During passage of the electron beam at a picture element spot, the co-ordinates of the next picture element spot are determined to calculate the focal distance. From the co-ordinates of four confirmation points surrounding the picture element spot of which the focal distance is to be determined, and the focal distance information, the sample surface is made into a quadratic surface in approximation to thereby determine the focal distance of the picture element spot. This construction enables obtaining a clear picture image even if the sample is inclined to have large irregularities, and enables effective examination of the surface irregularities.