Abstract: Laser lights L1 to L3 are relatively moved along a line to cut 5, while repeating a converging step of simultaneously converging the laser lights L1 to L3 at converging positions P1 to P3 separated from each other along the line 5. This forms a plurality of modified spots S along the line 5 and causes the plurality of modified spots S to form a modified region 7. The converging positions P1 to P3 in the repeated converging steps are kept from being superposed on each other, while at least one of converging positions P21 to P23 in the converging step in a later stage is located between converging positions P11 to P13 in the converging step in an earlier stage.

Abstract: Laser lights L1 to L3 are relatively moved along a line to cut 5, while repeating a converging step of simultaneously converging the laser lights L1 to L3 at converging positions P1 to P3 separated from each other along the line 5. This forms a plurality of modified spots S along the line 5 and causes the plurality of modified spots S to form a modified region 7. The converging positions P1 to P3 in the repeated converging steps are kept from being superposed on each other, while at least one of converging positions P21 to P23 in the converging step in a later stage is located between converging positions P11 to P13 in the converging step in an earlier stage.