A flash removing punch pin is provided with a rotating mechanism wherein a flange is formed on an upper end portion on an outer circumference side portion of a cutting edge portion, and a plurality of grooves are formed in the axis center direction to the side of a casting part from the flange. An inner portion is slidably inserted into an inner cover, and the inner portion and a processing portion are moved by a spring cylinder in a direction to be separated from each other. The spring cylinder is compressed when the punch pin is in proximity to the casting part, and then the flange of the punch pin contacts a flange portion of the casting part. When the inner portion slides into the inner cover, the processing portion rotates along the axis with the inner portion.