Surface inspection device, surface inspection method, and manufacturing method of metal strip

A surface inspection method of a metal strip, comprising:

• a first emission step of emitting light to a surface of a metal strip using a first light source unit;
• a first imaging step of imaging regular reflection light on the surface of the metal strip by emission light from the first light source unit using a first imaging unit;
• a second emission step of emitting light of a wavelength band different from that of the emission light of the first light source unit to the surface of the metal strip using a second light source unit, wherein the first light source unit and the second light source unit are arranged such that an incident angle of the emission light from the first light source unit differs from an incident angle of emission light from the second light source unit;
• a second imaging step of imaging irregular reflection light on the surface of the metal strip by the emission light from the second light source unit using a second imaging unit, wherein an optical axis of the first imaging unit with respect to a normal line of the metal strip and an optical axis of the second imaging unit with respect to the normal line of the metal strip differ;
• and
• a step of distinguishing a surface defect of the metal strip by using the regular reflection light imaged in the first imaging step and irregular reflection light imaged in the second imaging step, wherein
• the emission light from the first light source unit and the emission light from the second light source unit are simultaneously applied to a same place on the surface of the metal strip.