A control unit of a laser processing apparatus includes: a reference image storage section that images streets before formation of modified layers by an imaging unit and stores the captured image as a reference image; a calculation section that compares the reference image stored in the reference image storage section with an image of a wafer held by a chuck table that is captured by the imaging unit, and calculates the degree of agreement of the two images; and a decision section that decides whether the wafer is an unprocessed wafer not formed with the modified layers in the case where the degree of agreement calculated by the calculation section is more than a first predetermined value, and decides whether the wafer is a processed wafer formed with the modified layers in the case where the degree of agreement is equal to or less than a second predetermined value.