In this paper the concept of optical vortex scanning microscope (OVSM) is presented. In the OVSM a sample is scanned
by the focused laser beam with optical vortex. The beam possessing an optical vortex contains a line along which the
phase is undetermined. At image plane this line is seen as the single point. The position of such special singular point
(vortex points) changes when the beam is diffracted by a sample. The vortex point sensitivity is higher than the
sensitivity of the whole focused beam. In the OVSM the position of vortex point is traced while scanning the sample. In
this paper the behavior of focused vortex beam, when scanning the phase step is studied. This simple example illustrates
both the OVSM idea and the method for data analysis.