A substrate dividing method includes preparing a substrate that is formed with division start points along streets and that has a protective sheet attached to a surface on one side thereof and rolling a roller on a surface on the other side of the substrate, to attach an expanding tape. Next, suction by a holding table is cancelled, and, in a state in which a slight gap is formed between a holding surface of the holding table and the protective sheet, the roller is brought into contact with the expanding tape and rolled, thereby extending cracks extending from the division start points while causing the substrate to sink into the gap through the protective sheet with the division start points as starting points, and the expanding tape is expanded to widen the chip intervals with the division start points as starting points.