A defect marking device includes a flaw inspection device which has a plurality of light-receiving parts that identify reflected lights coming from an inspection plane of a metal strip under two or more of optical conditions different from each other; a signal processing section that judges the presence/absence of surface flaw on the inspection plane based on a combination of reflected light components identified under these optical conditions different from each other; and a marking device which applies marking that indicates information relating to the flaw on the surface of the metal strip.