An ellipsometer capable of improving a throughput calculating ellipsometry coefficients (ψ, Δ) even when performing measurement with a combination of a light source having a wide wavelength band and a spectrometer, and an apparatus for inspecting a semiconductor device is e hid g the ellipsometer may be provided. The ellipsometer includes a polarizing optical element unit for separating reflected light into two polarization components having polarization directions that are orthogonal to each other in a radial direction with respect to an optical axis of an optical system of the reflected light, an analyzer unit for transmitting components of a direction different from the polarization directions of the two polarization components to make the two polarization components interfere with each other, and to form an interference fringe in a form of a concentric circle, an image detector for detecting the interference fringe, and processing circuitry for calculating ellipsometry coefficients from the interference fringe.