A gathering operation includes a restraint operation of moving forward a left lower tool retention member so as to restrain a reference lower tool with the left lower tool retention member, an inserting operation of moving forward a right lower tool retention member so as to insert the right lower tool retention member into an insertion hole of a target lower tool, and an execution operation of moving the left and right lower tool retention members along a left-right direction so as to come close with each other. If a failure of the inserting operation is determined, a control device performs a retry operation of moving forward the right lower tool retention member again so as to insert the right lower tool retention member into the insertion hole (141) of the target lower tool after moving backward the left lower tool retention member.

A bending method utilizes a die including a V-groove at an upper part thereof, and a punch including a first surface and a second surface at a workpiece pressing portion. In a state of being mounted on an upper table of a press brake, the first surface is parallel to a first groove wall surface of the die mounted on a lower table. An angle formed between the second surface and a perpendicular plane is different from an angle formed between a second groove wall surface and the perpendicular plane. A plate-shaped workpiece placed on the die is bent in a state of being sandwiched between the first groove wall surface and the first surface.