Abstract: The present invention discloses an ellipsometer that is able to provide multivariable measurement and analysis of optical constants of sample, comprising: a semiconductor laser diode that serves as the light source; a Pertie device attached to the semiconductor laser diode; a collimator for making the light parallel; a polarizer for transforming the light into a suitable linearly polarized state and radiating onto the sample; an analyzer for converting the light reflected from the sample into suitable linearly polarized light; and, a photosensor; wherein, the wavelength of light radiated from the semiconductor laser can be changed by changing the case temperature of the semiconductor laser by a Pertie device. This ellipsometer is used to perform measurement using multiple wavelengths to obtain an initial model of the optical constants of each layer after which, by starting from this model, the optical constants of each layer are systematically calculated from measured values of tan .PSI. and cos .DELTA.