A device is provided for the optical detection of form errors of a low order, for example of roughness. The device possesses a light source whose light probes the body to be examined and a light-receiving device for the light reflected by the body. The device is characterized by the fact that the light-receiving device consists of a number of light-receiving elements arranged in linear array and that an evaluation unit determines the inclination angle of the probed surface element of the body from all output signals of the light-receiving elements. Shifts in the core of the reflected light beam can be measured which are substantially below the width of a light-receiving element. The measuring results remain practically unaffected by form deviations of a higher order such as roughness etc.