In this paper, we investigate the effect of a wide binary companion of the lens on the astrometric behavior of Galactic gravitational microlensing events and compare it to the effect on the photometric behavior. We find that the wide binary companion of the lens can affect the centroid motion of images substantially even if the corresponding light curve appears to be the one of a standard single point-mass lens event. The relatively significant effect of the wide binary lens on the astrometric lensing behavior, on one side, calls for careful consideration of the lens binarity in analyzing the future astrometric lensing data. On the other side, larger astrometric effect of the companion makes astrometric lensing an efficient method to detect binary lenses over a broad range of separations.

total 16 pages, including 5 figures and 2 tables, ApJ, submitted