A steel-strip production apparatus adapted to produce a hot-dip-plated steel strip and a cold-rolled steel strip, comprising: a continuous annealing furnace; a snout connected to the continuous annealing furnace; and a roll (31, 40) configured to turn the path direction of the steel strip after passing through the snout, wherein a hot-dip-plated steel strip production unit configured to produce the hot-dip-plated steel strip by bringing the steel strip continuously annealed in the continuous annealing furnace into the hot-dip-plating tank, and a cold-rolled steel strip production unit configured to produce the cold-rolled steel strip by transferring the steel strip continuously annealed in the continuous annealing furnace without causing the steel strip to pass through the hot-dip-plating tank are configured to be switchable with one another, wherein the roll (31, 40) configured to turn the path direction of the steel strip is a sink roll when producing the hot-dip-plated steel strip, and a deflector roll when producing the cold-rolled steel strip, and the steel-strip production apparatus selects the sink roll or the deflector roll in accordance with the type of the steel strip to be produced and installs the selected roll at a predetermined position, characterized in that the steel strip production apparatus further comprises: a contact-type seal plate device and a noncontact-type seal roll device that are arranged on the entry side of the snout along the transfer direction of the steel strip in this order, wherein the entry side of the snout is a portion in which the snout and the continuous annealing furnace are connected with each other; and a hot-dip-plating tank that is movable, wherein the immersion sink roll is located, during production of the hot-plated steal strip, at the same position as the deflector roll during the production of the cold-rolled steel strip. a continuous annealing furnace; a snout connected to the continuous annealing furnace; and a roll (31, 40) configured to turn the path direction of the steel strip after passing through the snout, wherein a hot-dip-plated steel strip production unit configured to produce the hot-dip-plated steel strip by bringing the steel strip continuously annealed in the continuous annealing furnace into the hot-dip-plating tank, and a cold-rolled steel strip production unit configured to produce the cold-rolled steel strip by transferring the steel strip continuously annealed in the continuous annealing furnace without causing the steel strip to pass through the hot-dip-plating tank are configured to be switchable with one another, wherein the roll (31, 40) configured to turn the path direction of the steel strip is a sink roll when producing the hot-dip-plated steel strip, and a deflector roll when producing the cold-rolled steel strip, and the steel-strip production apparatus selects the sink roll or the deflector roll in accordance with the type of the steel strip to be produced and installs the selected roll at a predetermined position, characterized in that the steel strip production apparatus further comprises: a contact-type seal plate device and a noncontact-type seal roll device that are arranged on the entry side of the snout along the transfer direction of the steel strip in this order, wherein the entry side of the snout is a portion in which the snout and the continuous annealing furnace are connected with each other; and a hot-dip-plating tank that is movable, wherein the immersion sink roll is located, during production of the hot-plated steal strip, at the same position as the deflector roll during the production of the cold-rolled steel strip. a contact-type seal plate device and a noncontact-type seal roll device that are arranged on the entry side of the snout along the transfer direction of the steel strip in this order, wherein the entry side of the snout is a portion in which the snout and the continuous annealing furnace are connected with each other; and a hot-dip-plating tank that is movable, wherein the immersion sink roll is located, during production of the hot-plated steal strip, at the same position as the deflector roll during the production of the cold-rolled steel strip.