For starting bending of a workpiece, a provisional drive end for a ram is computed from information such as processing conditions for the workpiece input through a processing (condition input section and the relationship between the target bending angle for the workpiece and the springback angle of the workpiece stored in a springback data section. The ram is driven to the provisional drive end and then the bending angle of the workpiece is measured thereat by an angle measuring unit. Thereafter, a final drive end for the ram is obtained from (i) the measured bending angle, (ii) the relationship between the bending angle of the workpiece and the amount of driving the ram stored in a bending angle vs. driving amount data section, and (iii) the relationship between the target bending angle for the workpiece and the springback angle of the workpiece stored in a springback data section. The ram is driven to the final drive end thus obtained to complete the bending operation.