To accurately detect the position of the seam part even it is an electric resistance welded tube the difference between the luminance signals of the seam part and the part other than the seam part of which is small.
In this device, the surface of the electric resistance welded tube P on which a marking is executed in the position at a prescribed distance from the seam position is imaged with a television camera 9. By binarizing the imaged two-dimensional image into the marking part where marking is put and the part other than the marking part and specifying the position of the marking part on the electric resistance welded tube P on the data which represent the position of the marking part where is discriminated from the binarized two-dimensional image and the position of the seam part S in the position at the prescribed distance from the marking part is detected.
YAMAMOTO MASAHIDE
MATSUOKA KAZUHIRO
