It is an object of the present invention to provide an optical-condition setting method for a charged-particle beam device, and the charged-particle beam device which make it possible to set the following optical condition: Namely, an optical condition which allows the suppression of a lowering in the measurement and inspection accuracy caused by the influence of electrification, even if there exist a large number of measurement and inspection points.In order to accomplish the above-described object, the following scanning electron microscope or optical-condition setting method is proposed: Namely, a scanning electron microscope or an optical-condition setting method for measuring a pattern on a sample based on the detection of electrons, the electrons being emitted from the sample by scanning the sample surface with an electron beam, wherein a change in measurement values relative to the number of measurements is determined from the measurement values at a plurality of measurement points on the sample, and the sample-surface electric field is controlled so that the inclination of the change becomes equal to zero, or becomes close to zero.