A planarization method includes a grinding step of holding the opposite side to a separation surface in an SiC ingot by a rotatable chuck table and rotating a grinding wheel having plural grinding abrasives disposed in a ring manner to grind the separation surface of the SiC ingot held by the chuck table, and a flatness detection step of irradiating the separation surface of the SiC ingot exposed from the grinding wheel with light and detecting reflected light to detect the degree of flatness. The grinding step is ended when that the separation surface of the SiC ingot has become flat is detected in the flatness detection step.