A method for treating lithium ion battery scrap containing Li, Ni, Co, Mn, Al, Cu and Fe, the method comprising carrying out a calcination step, a crushing step and a sieving step in this order, and after the steps, the method comprising: a leaching step of leaching the lithium ion battery scrap by adding it to an acidic solution to leave at least a part of Cu as a solid; a Fe/Al removal step comprising allowing a leached solution obtained in the leaching step to pass through a Fe removal process for separating and removing Fe by addition of an oxidizing agent and an Al removal process for separating and removing a part of Al by neutralization in any order; wherein the pH in the Fe removal process is from 3.0 to 4.0; wherein in the Al removal process the pH is from 4.0 to 6.0 and an oxidation-reduction potential, ORP vs Ag/AgCl, is from - 500mV to 100mV; and wherein when the Fe removal process is carried out before the Al removal process, an oxidation-reduction potential, ORP vs Ag/AgCl, is from 500mV to 1400mV, or; when the Fe removal process is carried out after the Al removal process, an oxidation-reduction potential, ORP vs Ag/AgCl, is from 300mV to 900mV; an Al/Mn extraction step of extracting and removing a residue of Al and Mn from a separated solution obtained in the Fe/Al removal step by solvent extraction; a Co recovery step of extracting and back-extracting Co from a first extracted solution obtained in the Al/Mn extraction step by solvent extraction and recovering the Co by electrolytic winning; a Ni recovery step of extracting and back-extracting, by solvent extraction, a part of Ni from a second extracted solution obtained by the solvent extraction in the Co recovery step and recovering the Ni by electrolytic winning; a Li concentration step of extracting and back-extracting, by solvent extraction, a residue of Ni and Li from a third extracted solution obtained by the solvent extraction in the Ni recovery step and repeating the operations of the extracting and the back-extracting to concentrate Li; and a Li recovery step of carbonating Li in a Li concentrated solution obtained in the Li concentration step to recover the Li as lithium carbonate. a leaching step of leaching the lithium ion battery scrap by adding it to an acidic solution to leave at least a part of Cu as a solid; a Fe/Al removal step comprising allowing a leached solution obtained in the leaching step to pass through a Fe removal process for separating and removing Fe by addition of an oxidizing agent and an Al removal process for separating and removing a part of Al by neutralization in any order; wherein the pH in the Fe removal process is from 3.0 to 4.0; wherein in the Al removal process the pH is from 4.0 to 6.0 and an oxidation-reduction potential, ORP vs Ag/AgCl, is from - 500mV to 100mV; and wherein when the Fe removal process is carried out before the Al removal process, an oxidation-reduction potential, ORP vs Ag/AgCl, is from 500mV to 1400mV, or; when the Fe removal process is carried out after the Al removal process, an oxidation-reduction potential, ORP vs Ag/AgCl, is from 300mV to 900mV; an Al/Mn extraction step of extracting and removing a residue of Al and Mn from a separated solution obtained in the Fe/Al removal step by solvent extraction; a Co recovery step of extracting and back-extracting Co from a first extracted solution obtained in the Al/Mn extraction step by solvent extraction and recovering the Co by electrolytic winning; a Ni recovery step of extracting and back-extracting, by solvent extraction, a part of Ni from a second extracted solution obtained by the solvent extraction in the Co recovery step and recovering the Ni by electrolytic winning; a Li concentration step of extracting and back-extracting, by solvent extraction, a residue of Ni and Li from a third extracted solution obtained by the solvent extraction in the Ni recovery step and repeating the operations of the extracting and the back-extracting to concentrate Li; and a Li recovery step of carbonating Li in a Li concentrated solution obtained in the Li concentration step to recover the Li as lithium carbonate.