A seamless steel pipe for line pipe, having a chemical composition comprising, in mass%: C: 0.02 to 0.11 %; Si: 0.05 to 1.0 %; Mn: 0.30 to 2.5 %; P: up to 0.030 %; S: up to 0.006 %; Cr: 0.05 to 0.36 %; Mo: 0.02 to 0.33 %; V: 0.02 to 0.20 %; Ti: 0.001 to 0.010 %; Al: 0.001 to 0.100 %; N: up to 0.008 %; Ca: 0.0005 to 0.0040 %; optionally Cu: 0 to 1.5 %; optionally Ni: 0 to 1.5 %; optionally Nb: 0 to 0.05 %; and balance Fe and impurities, the chemical composition satisfying Equation below, the steel pipe having a microstructure containing tempered martensite and/or tempered bainite and further containing ferrite in at least one of a portion between an outer surface of the steel pipe and a depth of 1 mm from the outer surface, and a portion between an inner surface of the steel pipe and a depth of 1 mm from the inner surface, wherein the proportion of the microstructure portions other than ferrite represented by tempered martensite and/or tempered bainite is 90 % or higher, in a cross section perpendicular to an axial direction of the steel pipe, an area ratio of ferrite at at least one of a depth of 1 mm from the outer surface of the steel pipe and a depth of 1 mm from the inner surface of the steel pipe is not lower than 5 % a Vickers hardness of a portion between a depth of 1 mm from the inner surface and a depth of 1 mm from the outer surface as measured in a wall thickness direction is not higher than 230 Hv, the Vickers hardness is measured in accordance with JIS Z 2244 where a testing force F is 98.07 N, and the seamless steel pipe has a yield strength not lower than 415 MPa, Cr + Mo + V ≤ 0.40 wherein each of the chemical symbols in equation is substituted for by the content of the corresponding element in mass%. C: 0.02 to 0.11 %; Si: 0.05 to 1.0 %; Mn: 0.30 to 2.5 %; P: up to 0.030 %; S: up to 0.006 %; Cr: 0.05 to 0.36 %; Mo: 0.02 to 0.33 %; V: 0.02 to 0.20 %; Ti: 0.001 to 0.010 %; Al: 0.001 to 0.100 %; N: up to 0.008 %; Ca: 0.0005 to 0.0040 %; optionally Cu: 0 to 1.5 %; optionally Ni: 0 to 1.5 %; optionally Nb: 0 to 0.05 %; and balance Fe and impurities, the chemical composition satisfying Equation below, the steel pipe having a microstructure containing tempered martensite and/or tempered bainite and further containing ferrite in at least one of a portion between an outer surface of the steel pipe and a depth of 1 mm from the outer surface, and a portion between an inner surface of the steel pipe and a depth of 1 mm from the inner surface, wherein the proportion of the microstructure portions other than ferrite represented by tempered martensite and/or tempered bainite is 90 % or higher, in a cross section perpendicular to an axial direction of the steel pipe, an area ratio of ferrite at at least one of a depth of 1 mm from the outer surface of the steel pipe and a depth of 1 mm from the inner surface of the steel pipe is not lower than 5 % a Vickers hardness of a portion between a depth of 1 mm from the inner surface and a depth of 1 mm from the outer surface as measured in a wall thickness direction is not higher than 230 Hv, the Vickers hardness is measured in accordance with JIS Z 2244 where a testing force F is 98.07 N, and the seamless steel pipe has a yield strength not lower than 415 MPa, Cr + Mo + V ≤ 0.40 wherein each of the chemical symbols in equation is substituted for by the content of the corresponding element in mass%. <EOS>