An optical scanning device includes a light source; a scanning unit to deflect/scan a laser beam from the light source; an imaging optical system to focus the deflected and scanned laser beam to a scan-target surface; an electro-optic element to electrically change a refractive index thereof; a controller to control the refractive index of the electro-optic element to adjust deflection amount of the laser beam; and a positional shift detecting unit, disposed away from the light path, to detect a positional shift of the incident laser beam from an ideal position in a sub-scanning direction. The device further includes a beam splitting element, and the controller adjusts a deflection amount of the laser beam from the electro-optic element based on a detection result by the positional shift detecting unit and corrects a positional shift in the sub-scanning direction of the laser beam on the scan-target surface.