PURPOSE: To restrain contamination sticking to a sample by interrupting image acquisition to suppress electron beam irradiation for searching a measuring point unless a predetermined significant change in an SEM image is recognized by an image change judging means.

CONSTITUTION: When an SEM image acquisition circuit 3 is started by user interface input of a work station 7, acquired SEM images are consecutively written in a frame memory. Unless a significant change in an SEM image is recognized by an SEM image change judging means 4, an interruption signal of image acquisition is output to the circuit 3 to interrupt image acquisition operation until change factor generation information on the SEM image, such as stage movement, magnification change, and optical parameter change, is inputted. Consequently, unnecessary electron beam irradiation onto a sample is suppressed so as to restrain contamination sticking thereto.