1. A method of dividing a wafer having projected dicing lines thereon by holding on a chuck table a wafer unit which includes the wafer adhered to an adhesive tape that is adhered to a ring frame in closing relation to an opening of the ring frame, with an exposed area in which the adhesive tape is exposed between an outer circumferential edge of the wafer and an inner circumferential edge of the ring frame, and fully severing the wafer by a cutting blade along the projected dicing lines, the method comprising: an exposed area incising step of lowering the cutting blade to a preset lowered position for fully severing the wafer to cause the cutting blade to incise the exposed area of the wafer unit; an image capturing step of capturing an image of an area incised by the cutting blade with image capturing means in the exposed area incising step; a determining step of determining whether or not it is possible to fully sever the wafer on the basis of the image captured in the image capturing step; and an adjusting step of increasing a distance by which to lower the cutting blade if it is determined that it is impossible to fully sever the wafer in the determining step.