Method and device for manufacturing black plated steel sheet

A method for manufacturing a black coated steel sheet by bringing steam into contact with a hot-dip Zn-Al-Mg alloy coated steel sheet under a closed atmosphere, the method comprising a step of, in a sealable chamber configured such that an amount of steam flowing into the sealable chamber and an amount of atmospheric gas flowing out of the sealable chamber are variably controllable, maintaining an internal pressure in the sealable chamber, while causing steam to flow into the sealable chamber through the use of a plurality of pipes, and causing atmospheric gas to flow out of the sealable chamber through the use of a plurality of pipes, in parallel with each other, so as to prohibit hydrogen gas generated in the sealable chamber from remaining therein, thereby to allow contact to occur between: the hot-dip Zn-Al-Mg alloy coated steel sheet; and the steam introduced into the sealable chamber.