To provide a plate bending die which is capable of performing the additional bending of the bending width larger than the die width, and hardly damages a plate.

The plate bending die 1 is abutted on a plate W to bend a plate piece Wa part by part in the bending width direction C. The plate bending die 1 has a blade-shaped bending blade 1a with a tip thereof abutted on the plate W. An end in the bending width direction C at the tip of the bending blade 1a which also forms a corner part on the plate-abutting side is formed to be a projecting curved part 1aa.