A method of processing a workpiece with a disk-shaped blade containing abrasive grains includes the steps of placing an auxiliary plate made of a material having a modulus of elasticity higher than a material of which a front surface side of the workpiece is made, on the front surface side of the workpiece, causing the blade rotated to cut into the front surface side of the workpiece to cut the workpiece as well as the auxiliary plate, and removing the auxiliary plate from the workpiece that has been cut by the blade.