Surface inspection device, surface inspection method, method of manufacturing steel material, method of managing quality of steel material, and manufacturing facility for steel material

A surface inspection method comprising:

• an irradiating step of emitting oblique illumination light beams onto a same inspection target region of steel material using two or more oblique line light sources;
• an imaging step of receiving each of reflected light beams of the oblique illumination light beams from the respective oblique line light sources, the reflected light beams being from the inspection target region for each oblique line light source, and capturing images of the inspection target region, by one or more line sensors;
• and
• a detecting step of detecting a linear surface defect at the inspection target region using the images captured at the imaging step, wherein
• orthographic projections of at least two oblique illumination light beams, out of the oblique illumination light beams from the two or more oblique line light sources, onto a surface of the steel material are orthogonal to each other on the inspection target region, and
• the two or more oblique line light sources are configured to emit the oblique illumination light beams in a direction oblique to a transport direction of the steel material.