PURPOSE: To easily, accurately and quickly carry out the bending with a good detecting accuracy by providing an adjusting function for a focal position and focal distance to a visual sensor of a bending angle correcting device so that they can be adjusted automatically.

CONSTITUTION: When the work W is bent by the cooperation of an upper die 13 and a lower die 9, the distance between the end face part of the work W and a picture pickup means is detected by a distance detecting means in a visual sensor 17. The focal distance and the focal position are adjusted automatically by a focal distance adjusting means and a focal position adjusting means provided in the visual sensor based on the detected distance. After this adjustment the shape of the end face of the work is picked by a picture pickup means and the present bending angle of the work W is detected by a bending angle detecting means in a picture processor 19 based on this picture. The die is corrected by a bending angle correcting means in the above device 19 through an NC device 21 based on this detecting angle and a target bending angle. By this method, the detecting accuracy is improved and the working accuracy is improved.