TWI731147B

[Problem] To provide practical technology for achieving the ability to identify a corner position for a rectangular substrate with high precision. [Solution] A camera 4 takes an image of an imaging area 41 after a rectangular substrate S is positioned such that a corner is positioned within the imaging area 41 for the camera 4. When the substrate S is determined to have a corner within the imaging area 41 by a blob Bs detected by binarizing image data, the outermost boundary points P from dark to light in the X direction scan lines Lx are made X direction edge point candidates, and the outermost boundary points P from dark to light in the Y direction scan lines Ly are made Y direction edge point candidates. The intersection of an approximate line passing through the X direction edge point candidates and an approximate line passing through the Y direction edge point candidates is identified as the substrate corner C position.