Method of dividing workpiece

A method of dividing a workpiece, the workpiece having on its surface a device formation region in which devices are formed in regions demarcated by a plurality of planned dividing lines formed in a grid pattern and a device non-formation region which surrounds the device formation region, the method comprising the steps of:

• irradiating the device non-formation region with a pulsed laser beam having such a wavelength as to be transmitted through the workpiece, thereby to form a pre-machining alteration region in the inside of the workpiece in the device non-formation region, wherein said irradiating stops prior to reaching the device formation region such that the pre-machining alteration region is not formed between adjacent devices;
• imaging the pre-machining alteration region by imaging means using infrared rays, thereby to detect a deviation between the position of irradiation with the laser beam and the position of the planned dividing line as machining position correction information;
• and
• correcting the position of irradiation with the laser beam on the basis of the machining position correction information and irradiating the workpiece with a pulsed laser beam having such a wavelength as to be transmitted through the workpiece, along the planned dividing line, to thereby form a main machining alteration region serving as a starting point of division.