Method for pickling steel plate and pickling apparatus

A pickling apparatus for pickling a steel plate having a first steel plate portion and a second steel plate portion which is connected to a tail end of the first steel plate portion and which requires a longer time for pickling than the first steel plate portion when pickled under the same condition, comprising:

• at least one pickling tank storing an acid solution;
• a conveyance part configured to convey the steel plate while immersing the steel plate in the acid solution in the at least one pickling tank;
• a circulation line for circulating the acid solution inside any of the at least one pickling tank, the circulation line being connected to the at least one pickling tank;
• an oxidizing device disposed in the circulation line and configured to oxidize Fe2+ in the acid solution to Fe3+ by using a gaseous oxidant;
• and
• a liquid oxidant feeding part capable of feeding a liquid oxidant for oxidizing Fe2+ in the acid solution to Fe3+ to any one of the at least one pickling tank or to the circulation line,
• wherein the liquid oxidant feeding part is configured to, upon switching from pickling of the first steel plate portion to pickling of the second steel portion, start feeding of a liquid oxidant for oxidizing Fe2+ in the acid solution to Fe3+ to any of the at least one pickling tank or to the circulation line.