The present invention is a birefringence measuring device that requires only three types of light intensity information and can measure birefringence characteristics of an object with a relatively inexpensive device configuration. One embodiment comprises a light source for emitting a light flux having a specific polarization state towards the object to be measured, an optical system for extracting each of light fluxes in predetermined three polarization direction; and, from the light flux having passed the object to be measured, a detector for detecting a light amount of each of the light fluxes in the predetermined three polarization directions extracted by the optical system, and a processor for calculating a size and an azimuth of the birefringence of the object to be measured. The processor may calculate the birefringence size and azimuth by assigning each of the light amounts of the light fluxes detected by the detector to a predetermined function expression.