While reliably cutting an object to be processed, the strength of the resulting chips is improved. An object to be processed 1 is irradiated with laser light L, so as to form modified regions 17, 27, 37, 47 extending along lines to cut 5 and aligning in the thickness direction in the object 1. Here, modified regions 17 are formed such that modified region formed parts 17a and modified region unformed parts 17b alternate along the lines, and modified regions 47 are formed such that modified region formed parts 47a and modified region unformed parts 47b alternate along the lines. This can inhibit formed modified regions 7 from lowering the strengths on the rear face 21 side and front face 3 side of chips obtained by cutting. On the other hand, modified regions 27, 37 located between the modified regions 17, 47 are formed continuously from one end side of the lines 5 to the other end side thereof, whereby the cuttability of the object 1 can be secured reliably.