A workpiece processing device includes a workpiece supporting unit configured to support a workpiece so that the workpiece is rotatable around a first axis parallel to a central axis of the workpiece, a cutting unit having a blade configured to cut a surface of the workpiece, a detecting unit configured to calculate a position of a vertex of the surface in a direction along a second axis which is perpendicular to the first axis and parallel to the blade, and a control unit configured to control the workpiece supporting unit so that a cutting position on the surface is located at a vertex in the direction along the second axis, and relatively move the workpiece supporting unit and the cutting unit so that an incision direction of the blade is on a plane defined by the central axis and the cutting position, thereby forming a groove at the cutting position.