CARDBOARD SHEET DEFECT DETECTION DEVICE, CARDBOARD SHEET DEFECT REMOVAL DEVICE, AND CARDBOARD SHEET PRODUCTION DEVICE

A cardboard sheet defect detection device, a cardboard sheet defect removal device, and a cardboard sheet production device that comprise: an illumination device (51) that shines parallel light toward a corrugated medium (B) at an illumination angle (θ1) that is sloped at exactly a preset prescribed angle relative to a perpendicular (L1) to a single-sided cardboard sheet (D) ; an imaging device (52) that captures images of the portion of the corrugated medium (B) that is illuminated by the parallel light; a shaded image processing device (57) that, on the basis of the images captured by the imaging device (52), defines a bright region (W) or a dark region (G) along a transport direction for the single-sided cardboard sheet (D); and a determination device (58) that makes determinations on quality by comparing the length (W1) of the bright region W or the length (G1) of the dark region (G) as defined by the shaded image processing device (57) with a preset determination value.