A method for removing phosphorus from a phosphorus-containing substance in which the phosphorus-containing substance that is used as a raw material for metal smelting or metal refining is reacted with a nitrogen-containing gas so that phosphorus in the phosphorus-containing substance is removed through nitriding, characterized in that prior to a nitriding removal of phosphorus from the phosphorus-containing substance, a reduction treatment is performed in which the phosphorus-containing substance is heated to an unmolten state temperature range so as to react with a reducing agent, thereby reducing at least a part of metal oxide in the phosphorus-containing substance, wherein a reduction ratio of iron oxide and manganese oxide in the phosphorus-containing substance at an end of the reduction treatment is set to not less than 11% and less than 33%, wherein the iron oxide represents any of or a mixture of FeO, Fe 3 O 4 , and Fe 2 O 3 , the manganese oxide represents any of or a mixture of MnO, Mn 3 O 4 , Mn 2 O 3 , and MnO 2 , and the reduction ratio refers to a ratio of an amount of oxygen removed by reduction to total oxygen in the iron oxide and the manganese oxide, wherein the reducing agent is a reducing gas or a solid reducing agent, and wherein the reduction treatment using the reducing gas is performed in a range of Expression below: [Expression 2] 1.5 ≦ x × Q ≦ 6.0 wherein x denotes twice (-) a volume ratio of an oxygen gas in a standard state required for complete combustion of a unit volume of the reducing gas in the standard state, and Q denotes an amount of the reducing gas (Nm 3 /kg) used for the reduction treatment with respect to a total amount of the iron oxide and the manganese oxide in the phosphorus-containing substance. prior to a nitriding removal of phosphorus from the phosphorus-containing substance, a reduction treatment is performed in which the phosphorus-containing substance is heated to an unmolten state temperature range so as to react with a reducing agent, thereby reducing at least a part of metal oxide in the phosphorus-containing substance, wherein a reduction ratio of iron oxide and manganese oxide in the phosphorus-containing substance at an end of the reduction treatment is set to not less than 11% and less than 33%, wherein the iron oxide represents any of or a mixture of FeO, Fe 3 O 4 , and Fe 2 O 3 , the manganese oxide represents any of or a mixture of MnO, Mn 3 O 4 , Mn 2 O 3 , and MnO 2 , and the reduction ratio refers to a ratio of an amount of oxygen removed by reduction to total oxygen in the iron oxide and the manganese oxide, wherein the reducing agent is a reducing gas or a solid reducing agent, and wherein the reduction treatment using the reducing gas is performed in a range of Expression below: [Expression 2] 1.5 ≦ x × Q ≦ 6.0 wherein x denotes twice (-) a volume ratio of an oxygen gas in a standard state required for complete combustion of a unit volume of the reducing gas in the standard state, and Q denotes an amount of the reducing gas (Nm 3 /kg) used for the reduction treatment with respect to a total amount of the iron oxide and the manganese oxide in the phosphorus-containing substance. <EOS>