A wafer dividing method for dividing a wafer having a film on the front side thereof. The wafer dividing method includes a modified layer forming step of applying a laser beam having a transmission wavelength to the substrate of the wafer from the front side thereof along the streets so that a focal point of the laser beam is set inside the substrate, thereby forming a modified layer in the substrate along each street, a film dividing step of applying a laser beam having an absorption wavelength to the film from the front side of the wafer along each street to thereby form a laser processed groove for dividing the film along each street, a back grinding step of grinding the back side of the substrate of the wafer to thereby reduce the thickness of the wafer to a predetermined thickness, a wafer supporting step of attaching the wafer to a dicing tape supported to an annular frame, and a wafer breaking step of applying an external force to the wafer by expanding the dicing tape to thereby break the wafer along each street.