To extend and divide a plate-shaped work formed with a metallic layer on a substrate after irradiating the substrate with a laser beam.

After a degeneration layer 7 is formed along a division scheduled line 2 inside a wafer 1 in a work 10 having a double-layer structure formed with a solder layer (metallic layer) 5 on a back face 1b of a wafer (substrate ) 1, and then the work 10 is folded along a division scheduled line 2, and the wafer 1 is divided with the degeneration layer 7 as a start point in this stage, and a weak section 8 is formed in the solder layer 5. Then, a tape 12 for extension is extended, an external force is added to the solder layer 5, the solder layer 5 is divided with the weak point 8 as the start point, and the work 10 is completely divided.