a light source generating light beam;

a lens focusing the light beam emitted from the light source to form a light spot on a sample surface;

an optical dividing element dividing the light beam reflected from the sample surface or transmitted through the sample into a plurality of different light beams;

a first photodetector receiving a first light beam divided by the optical dividing element to output a first output signal based on a beam amount of the received beam;

a second photodetector receiving a second light beam divided by the optical dividing element to output a second output signal based on a beam amount of the received beam;

a defect candidate detection part detecting a defect candidate based on the first output signal and the second output signal to output a first defect candidate signal and a second defect candidate signal; and

a real defect determination part determining the defect candidate as a real defect upon detecting the first defect candidate signal and the second defect candidate signal within a certain period of time;

wherein the optical dividing element is disposed at a position to divide the light beam substantially in half in a direction orthogonal to an optical axis of the light beam when the light beam is reflected from a region having no defects on the sample, and

wherein the optical dividing element divides the light beam by changing a propagation direction of the light beam which is made incident on the optical dividing element into different propagation directions.