A method of dividing a workpiece includes: forming a pre-machining alteration region in the inside of a region in which no device is formed; detecting the position of the pre-machining alteration region through infrared imaging by imaging means, to thereby recognize a deviation between the pre-machining alteration region and a planned dividing line as machining position correction information; and forming a main machining alteration region by utilizing the machining position correction information, whereby the workpiece can be accurately divided along the planned dividing lines into individual devices.