PURPOSE: To shorten the cycle time and to improve the productivity by changing holding part from one side to another side of a metal sheet to be clamped in a next process during a period from the start of bending the metal sheet to the end of it.

CONSTITUTION: At the time point of holding a metal sheet WK attached to a robot hand 1 between a punch 4 and a die 5, the state of holding with a finger 2 is released. Holding part is changed from the side of front face to the side of lateral direction by moving he hand 1. At the time point of finishing bending the metal sheet WK with the punch 4, the finger 2 again closes and holds the metal sheet WK. The hand 1 is moved upward, further moved to the front of the press brake and the bent metal sheet WK is taken out from the press brake. Therefore, in the next process, the side to be bent next can be immediately bent.