In a continuous casting device (100) for casting stainless steel slabs (3c), a long nozzle (2) extending into a tundish (101) is provided on a ladle (1). Molten stainless steel (3) is poured through the long nozzle (2) into the tundish (101), and the spout (2a) of the long nozzle (2) is immersed in the poured molten stainless steel (3). During pouring, an argon gas (4a) is supplied around molten stainless steel (3) in the tundish (101). Further, while immersing the spout (2a) of the long nozzle (2) in the molten stainless steel (3) in the tundish (101), the molten stainless steel (3) is poured from the ladle (1) into the tundish (101) and poured from the tundish (101) into a casting mold (105), allowing continuous casting. During casting, a nitrogen gas (4b) is supplied instead of the argon gas (4a) around the molten stainless steel (3) inside of the tundish (101).