To provide an ellipsometer capable of accurately measuring a measuring object in vacuum atmosphere, and even when an optical fiber is attached/detached, capable exerting no influence on measurement accuracy.

A light projection part 13 and a light receiving part 14 are arranged on the inside of a housing 11, a light-emitting device 12 is arranged on the outside of the housing 11, and the light-emitting device 12 and the light projection part 13 are optically connected to each other by an optical wiring device 18. When the light projection part 13 polarizes incident light to generate measurement light and applies the measurement light to a measuring object 7 and the light receiving part 14 receives reflected light and sends the received reflected light to an analyzer 15 arranged on the outside of the housing 11, the analyzer 15 finds film thickness. Thus, the measuring object 7 can be measured in vacuum atmosphere, and even when the optical wiring device 18 and the light projection part 13 are attached/detached, these units can be temporarily fixed relatively on the same positions and the attachment/detachment does not exert influence on the measurement accuracy.