STEEL PLATE INSPECTION APPARATUS AND STEEL PLATE INSPECTION METHOD

PROBLEM TO BE SOLVED: To perform visualized inspection of a magnetic domain structure of a steel plate continuously without stopping a manufacturing line.SOLUTION: A steel plate inspection apparatus 1 according to the present invention comprises: a central shaft 3 bridged in a plate width direction of a steel plate 2 in a manufacturing line; a roll 4 rotating around the central shaft 3 while pressing the steel plate 2 so that a distance between the steel plate 2 and the central shaft 3 is kept constant; a magnetooptical element 5 that is placed close to the steel plate 2 and can detect a magnetic domain structure of the steel plate 2 as optical characteristics; a fixture 6 that is fixed on the central shaft 3 and makes the a magnetooptical element 5 keep a constant distance from the central shaft 3; a light source for irradiating the magnetooptical element 5 with linear polarization; and a detector 7 for detecting the linear polarization whose polarization plane is rotated in accordance with the magnetic domain structure of the steel plate 2 that has been transcribed to the magnetooptical element 5.