In bending a workpiece (W), a position of the workpiece W relatively pressed down by a punch (P) is directly detected by a plurality of position detection means (RDC1, RDC2 and RDC3) provided in a V-groove (11) of a die, and a bending speed calculation section obtains a bending speed from a change in this position. If bending speeds at position of the respective position detection means differ, a uniform speed arithmetic operation section calculates a bending speed to make the bending speeds at the positions of all of the position detection means uniform, and a driving shaft instruction section controls driving shafts (7L, 7R) to bend the workpiece at the uniform bending speed.