An object of the present invention to provide a method of cutting a workpiece while restraining the production of surface chippings and at the same time preventing offcut chips from being formed on anouter peripheral extra area of the workpiece. There is provided a method of cutting a plate-shaped workpiece having on a face side thereof a device area that is demarcated by a grid of projected dicing lines into a plurality of subareas where respective devices are formed, and an outer peripheral extra area surrounding the device area, to form cut grooves having a predetermined depth in the device area of the workpiece. The method includes: a guide groove forming step of forming a guide groove to a depth smaller than a predetermined depth in the workpiece, causing a cutting blade to cut intothe workpiece held on the holding surface of the chuck table from an outer peripheral edge of the workpiece along one of the projected dicing lines; and a device area processing step of forming a groove to the predetermined depth in the workpiece along the projected dicing line, the groove extending from the device area beyond an opposite end of the device area to a portion of the outer peripheralextra area, after lowering the cutting blade toward and into the guide groove in the device area and then positioning a cutting edge thereof at the predetermined depth.