The angle measuring device has a laser (1), an interferometer module (2) with a beam splitter (3) and optical elements for providing parallel partial beams (14,15). A rotatable element (11) with a refraction grating (12) provides an optical path difference dependent on the angular position. The diffraction grating has equidistant line structures parallel to a diagonal of the rotatable element, with the grating plane perpendicular to the central rotation axis (10). The transmitted light is reflected by a rear surface (18) at an angle to this axis. The lattice constant of the grating is dimensioned so that the angle of deflection of the first or higher diffraction order of the partial beams corresponds to the slope of the rear surface.
