An optical reading head of a scanning apparatus includes a casing, a lens, a base and a sliding frame. The base is used to support an image sensing module and movable on the casing. The sliding frame is coupled with the base for fixing and driving the lens to move along a gliding track on the casing. During the focusing operation, the lens' position is adjustable by moving the sliding frame and the optical signals are clearly imaged onto the image sensor of the imaging sensing module. During the magnification correcting operation, positions of the lens and the imaging sensing module are adjustable by moving the base and the tolerance of magnification for the optical reading head would be equal to or less than an acceptable preset value.