PURPOSE: To provide inclination measuring instrument that allows the reflection points of measuring light on a reflecting surface to be changed.

CONSTITUTION: The title inclination measuring instrument 10 includes a plurality of optical measuring mechanisms each of which consists of a pair of a light projecting optical system and a light receiving optical system. Each of the light projecting optical system consists of a light source 12 that turns measuring light into parallel rays and projects the rays; and a mirror 16 that reflects the measuring light projected from the light source and directs it to a wafer. Each of the light receiving optical system consists of a mirror 18 that receives the measuring light reflected by the wafer; and a sensor 28 that determines the properties of the measuring light, passed through the mirror and received. Thus the properties of measuring light reflected at different points are compared, and the inclination of the wafer, placed on a wafer table, is thereby determined. In addition first parallel light transmitting plates 30 are placed behind the light projecting optical systems' mirrors 16 of the inclination measuring instrument as viewed in the direction of the travel of light. Second parallel flat light transmitting plates 32 are placed before the light receiving optical systems' mirrors 18. These plates can be freely rotated by means of driving apparatuses. This makes the positions of reflection points shiftable.