Provided are a workpiece dividing device and a workpiece dividing method that are capable of solving a problem in which division is not performed along a scheduled division line and which occurs when the chip size is small. A frame 4 of a wafer unit 2 is fixed by means of a frame fixing section 12 of an expansion restricting ring 16. Next, an expand ring 14 is moved upward so as to start the expansion of the whole area of an annular area 3B. Next, when the upward movement amount of the expand ring 14 exceeds the thickness of the frame 4, the annular area 3B makes contact with an expansion restriction section 17, and the expansion of an outer circumferential area 3E located on the outer circumferential side of the annular area 3B is restricted. Next, upward movement of the expand ring 14 is continued and expansion of an inner circumferential area 3F excluding the outer circumferential area 3E in the annular area 3B is continuously performed, so that a wafer 1 is divided into individual chips 6.