To provide a compact general purpose microscopic inclination detector of an optical lever type, having high sensitivity of an inclination angle resolution of about 10-5 rad or better.

A semiconductor laser is used for making a detector small, size, the optical path length of reflected light is extended with a mirror to about 100 mm, and a semiconductor laser beam that tends to diverge is almost focused on a measuring surface with a lens to obtain a high sensitivity. The sensitive microscopic inclination detector having a small size of 91×37×25(mm3) or 91×30×25(mm3) and a microscopic inclination angle resolution of 10-5 rad or better can be obtained.