A method of manufacturing a duplex seamless stainless steel pipe using an apparatus line for manufacturing seamless steel pipes and tubes, the apparatus line comprising: a heating apparatus for heating a steel raw material; a piercing apparatus for piercing the heated steel raw material thus forming a hollow material; a rolling apparatus for applying hot working to the hollow material thus forming a seamless steel pipe having a predetermined size; and a cooling apparatus arranged on an exit side of the rolling apparatus, wherein a steel raw material is heated by the heating apparatus, the hollow material is formed by piercing the steel raw material by the piercing apparatus, the hollow material is formed into a hollow piece by applying hot working by the rolling apparatus, the hollow piece is cooled by the cooling apparatus, and the steel material has the composition which contains, by mass%, 0.050% or less C, 2.00% or less Si, 5.00% or less Mn, 0.05% or less P, 0.03% or less S, 16.0 to 35.0% Cr, 3.0 to 12.0% Ni, 5.0% or less Mo, 0.1% or less Al, 0.5% or less N, and optionally one, two or more of 3.0% or less Nb, 0.1% or less Ti, 3.0% or less V, 0.5% or less Zr, 3.5% or less W, 3.5% or less Cu, 0.05% or less REM, 0.01% or less B, and 0.1% or less Ca, and Fe and an unavoidable impurities as a balance, wherein as unavoidable impurities 0.0050% or less O is permissible, wherein the steel raw material is heated to a temperature of (δ A -300°C) to (δ A +100°C)by the heating apparatus, hot working is applied to the hollow material by the rolling apparatus, and using a surface temperature of the hollow piece before being cooled by the cooling apparatus as a cooling start temperature, the cooling apparatus cools the hollow piece to a cooling stop temperature having a temperature difference of at least 50°C or more from the cooling start temperature in terms of an outer surface temperature and being equal to or above 600°C in terms of a wall thickness center temperature at an average cooling speed of 3°C/s or more in terms of an outer surface temperature, and wherein after stopping cooling, the average cooling speed at a position on an outer surface of the hollow piece is adjusted to 1.0°C/s or less, wherein duplex stainless steel is high-chromium stainless steel having a multiphase structure having at least two phases consisting of a ferrite phase and an austenite phase in a temperature region for hot working of pipes and tubes. a heating apparatus for heating a steel raw material; a piercing apparatus for piercing the heated steel raw material thus forming a hollow material; a rolling apparatus for applying hot working to the hollow material thus forming a seamless steel pipe having a predetermined size; and a cooling apparatus arranged on an exit side of the rolling apparatus, wherein a steel raw material is heated by the heating apparatus, the hollow material is formed by piercing the steel raw material by the piercing apparatus, the hollow material is formed into a hollow piece by applying hot working by the rolling apparatus, the hollow piece is cooled by the cooling apparatus, and the steel material has the composition which contains, by mass%, 0.050% or less C, 2.00% or less Si, 5.00% or less Mn, 0.05% or less P, 0.03% or less S, 16.0 to 35.0% Cr, 3.0 to 12.0% Ni, 5.0% or less Mo, 0.1% or less Al, 0.5% or less N, and optionally one, two or more of 3.0% or less Nb, 0.1% or less Ti, 3.0% or less V, 0.5% or less Zr, 3.5% or less W, 3.5% or less Cu, 0.05% or less REM, 0.01% or less B, and 0.1% or less Ca, and Fe and an unavoidable impurities as a balance, wherein as unavoidable impurities 0.0050% or less O is permissible, wherein the steel raw material is heated to a temperature of (δ A -300°C) to (δ A +100°C)by the heating apparatus, hot working is applied to the hollow material by the rolling apparatus, and using a surface temperature of the hollow piece before being cooled by the cooling apparatus as a cooling start temperature, the cooling apparatus cools the hollow piece to a cooling stop temperature having a temperature difference of at least 50°C or more from the cooling start temperature in terms of an outer surface temperature and being equal to or above 600°C in terms of a wall thickness center temperature at an average cooling speed of 3°C/s or more in terms of an outer surface temperature, and wherein after stopping cooling, the average cooling speed at a position on an outer surface of the hollow piece is adjusted to 1.0°C/s or less, wherein duplex stainless steel is high-chromium stainless steel having a multiphase structure having at least two phases consisting of a ferrite phase and an austenite phase in a temperature region for hot working of pipes and tubes.