Molten steel secondary refining method and steel production method

To provide a molten steel secondary refining method enabling nitrogen concentration to stably reach low nitrogen concentration zone at high speed without causing an operation problem, and a steel production method. A secondary refining method is provided in which an Al addition step of adding a metal Al-containing substance to molten steel to form Al-containing molten steel and a CaO addition step of adding a CaO-containing substance to molten steel are combined to form slag containing CaO and Al2O3, then an acid transfer treatment including a denitrification treatment in which oxygen-containing gas is blown to the Al-containing molten steel through the slag is performed, wherein based on the stirring power density [epsilon](W/t) upon slag formation, an Al concentration [Al]i(mass%) in the molten steel immediately before the acid transfer treatment is set to be a value [Al]e or more calculated by the following formula (A), and the Al concentration [Al]f at the end of the acid transfer treatment is set to be 0