A method of manufacturing a welded structure of a ferritic heat-resistant steel including a base material, a weld heat-affected zone and a weld metal, comprising: the step of preparing the base material, the base material having a chemical composition consisting of, in mass %: 0.05 to 0.12 % C; 0.02 to 0.45 % Si; 0.40 to 0.80 % Mn; 8.0 to 12.0 % Cr; 0.003 to 0.080 % N; 0.30 to 1.30 % Mo; 0.005 to 0.10 % Nb; 0.005 to 0.50 % V; 0 to 2.0 % W; 0 to 3.5 % Re; 0 to 0.15 % Ti; 0 to 0.15 % Zr; 0 to 0.0050 % Ca; 0 to 0.0050 % Mg; 0 to 0.0500 % Y; 0 to 0.0500 % Ce; and 0 to 0.0500 % La, Ni being limited to below 0.20 %, Cu below 0.20 %, B below 0.005 %, Al below 0.025 %, P below 0.020 %, S below 0.010 %, and O below 0.010 %, the balance being Fe and impurities; the step of forming an edge on the base material; a pre-weld heat treatment step in which a region located between a surface of the edge and a position distant from the surface of the edge by a pre-weld heat treatment depth of 30 to 100 mm is heated to a temperature of 1050 to 1200 °C and is held at this temperature for 2 to 30 minutes; a welding step in which, after the pre-weld heat treatment step, the edge is welded to form the weld metal; and a post-weld heat treatment step in which, after the welding step, a region located between the surface of the edge and a position distant from the surface of the edge by a distance not smaller than the pre-weld heat treatment depth and not greater than 100 mm is heated to a temperature of 720 to 780 °C and is held at this temperature for a time period not shorter than 30 minutes and satisfying the following formula,: Log t + 12 ⋅ T + 273 < 13810 where t is the holding time and T is the temperature; the unit of t is hour and the unit of T is °C; and Log is the common logarithm. 0.05 to 0.12 % C; 0.02 to 0.45 % Si; 0.40 to 0.80 % Mn; 8.0 to 12.0 % Cr; 0.003 to 0.080 % N; 0.30 to 1.30 % Mo; 0.005 to 0.10 % Nb; 0.005 to 0.50 % V; 0 to 2.0 % W; 0 to 3.5 % Re; 0 to 0.15 % Ti; 0 to 0.15 % Zr; 0 to 0.0050 % Ca; 0 to 0.0050 % Mg; 0 to 0.0500 % Y; 0 to 0.0500 % Ce; and 0 to 0.0500 % La, Ni being limited to below 0.20 %, Cu below 0.20 %, B below 0.005 %, Al below 0.025 %, P below 0.020 %, S below 0.010 %, and O below 0.010 %, the balance being Fe and impurities; the step of forming an edge on the base material; a pre-weld heat treatment step in which a region located between a surface of the edge and a position distant from the surface of the edge by a pre-weld heat treatment depth of 30 to 100 mm is heated to a temperature of 1050 to 1200 °C and is held at this temperature for 2 to 30 minutes; a welding step in which, after the pre-weld heat treatment step, the edge is welded to form the weld metal; and a post-weld heat treatment step in which, after the welding step, a region located between the surface of the edge and a position distant from the surface of the edge by a distance not smaller than the pre-weld heat treatment depth and not greater than 100 mm is heated to a temperature of 720 to 780 °C and is held at this temperature for a time period not shorter than 30 minutes and satisfying the following formula,: Log t + 12 ⋅ T + 273 < 13810 where t is the holding time and T is the temperature; the unit of t is hour and the unit of T is °C; and Log is the common logarithm.