A pump beam irradiates the surface of a semiconductor sample through modulator while irradiating the surface with a probe beam so that a detector measures a light-modulated spectrum of the probe beam reflected from the surface of the semiconductor sample. Then, surface electric field strength is calculated from the period of Franz-Keldysh oscillations appearing in the light-modulated spectrum, and the surface recombination velocity and surface Fermi level are calculated based on a relation between the surface electric field strength and the probe beam power density.