A method of cutting a workpiece includes forming a guide groove to a depth smaller than the predetermined depth in the workpiece, the guide groove extending from the outer peripheral edge to an end portion of the device area, by causing a cutting blade to cut into the 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 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 peripheral extra 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.