To provide a non-invasive glucose measuring apparatus for a living body, which has not been put into practical use heretofore.

In order to achieve the object, this apparatus for measuring optical rotation characteristic of a living body adopts a method of causing wavelength-turnable laser beam synchronized with pulses to enter the living body through a plane of polarization preserving optical fiber limited in its length so that the output light periodically changes in lateral circularly polarized light state.