To provide an auxiliary die for work holding capable of bending even in the case of a special bending side having a main body part subjecting to normal hemming to the auxiliary die and a flange part crossing for a bending side.

Relating to a bending machine BM of a plate material, etc., an auxiliary die KH mounted to the rear face of an upper die Dt through a horizontal member Ph is constituted of a main body 1 and a mounting/ demounting change unit part 2, a cavity part 1a approximated to a halved cylindrical shape is arranged near a lower part center of the upper die Dt along the left/right longitudinal direction so as to enable normal hemming, further, the mounting/demounting change unit part 2 is positioned in a bending region and has a shape coping with hemming of a work having a flange part crossing a bending side of the work W.