A size of particle or defect in an object is measured. A laser beam is guided through an optical system into the object. A light receiving element receives scattered light from a particle or a defect in the object. A scattering image is formed by an image processor from the scattered light thus received. The size of particle or defect is obtained by integrating a scattering intensity of the scattered light. Also, a size distribution of particle or defect in an object may be acquired by detecting a maximum scattering intensity of each particle or defect. A polarization dependency of scattering may be checked as well.