When work is to be bent by cooperation between a punch and a die, a temporary stroke value for obtaining a predetermined angle is determined on the basis of bending conditions. Trial bending is effected using the temporary stroke value, and the re-striking frequency with which the work is re-struck till a predetermined angle is obtained is discriminated. Since the re-striking frequency and the amount of correction of stroke value for the regular bending corresponding to the predetermined angle have been found in advance, the regular bending is effected by calculating the corresponding amount of correction of stroke value on the basis of the first-mentioned amount of correction of stroke value to provide a corrected stroke value for the regular bending.
