PURPOSE: To detect micro-displacement angles with a small size and high accuracy by amplifying the angular displacements of a turning reflection member by the use of multiple reflections between a stationary reflection member and the turning reflection member facing the same.

CONSTITUTION: A reflecting mirror 1 suspended by a stationary member 2 has reflection surfaces 1a, 1b, and is located in a stationary reflecting mirror 3 having four reflection surfaces 3aW3d. The light from a light source 4 passes through a pinhole 5 and a condenser lens 6 and reflects alternately between both reflecting mirrors mentioned above and forms images on one-dimensional image sensors 9 through a prism 7 and an imaging lens 8. When the member 2 inclines by θ from the vertical direction, the mirror 1 displaces from the mirror 3 and the inclination of the luminous flux made incident to the prism changes largely. When it reflects n times between both reflecting mirrors, the incident angle to the prism changes by 2nθ. This is detected from the extent at which the pinhole image moves on the sensors 9.