A forging steel excellent in forgeability comprising, in mass%: C: 0.001 to less than 0.05%, Si: 0.7% or less, Mn: 0.01 to 4.0%, Cr: 5.0% or less, Nb: 0.005 to 0.1%, P: 0.2% or less, S: 0.35% or less, Al: 0.0001 to 2.0%, N: 0.016% or less, one or both of Mo: 1.5% or less (including 0%) and Ni: 4.5% or less (including 0%); wherein Di given by the following Equation is 60 or greater: wherein Di given by the following Equation 1 is 60 or greater: Di = 5.41 × Di Si × Di Mn × Di Cr × Di Mo × Di Ni × Di Al where Di Si = 0.7 × % Si + 1, Di Mn = 3.335 × % Mn + 1 when Mn ≤ 1.2 %, Di Mn = 5.1 × % Mn − 1.12 when 1.2 % < Mn, Di Ni = 0.3633 × % Ni + 1 when Ni ≤ 1.5 % Di Ni = 0.442 × % Ni + 0.8884 when 1.5 % < Ni ≤ 1.7, Di Ni = 0.4 × % Ni + 0.96 when 1.7 % < Ni ≤ 1.8, Di Ni = 0.7 × % Ni + 0.42 when 1.8 % < Ni ≤ 1.9, Di Ni = 0.2867 × % Ni + 1.2055 when 1.9 % < Ni, Di Cr = 2.16 × % Cr + 1, Di Mo = 3 × % Mo + 1, Di Al = 1 when Al ≤ 0.05 %, and Di Al = 4 × % Al + 1 when 0.05 % < Al, a symbol in brackets [] indicating content (mass%) of the element concerned, the forging steel optionally comprising, in mass%: Cu: 0.6 to 2.0%, wherein Di given by the following Equation instead of Equation is 60 or greater: Di = 5.41 × Di Si × Di Mn × Di Cr × Di Mo × Di Ni × Di Al × Di Cu where Di(Si), Di(Mn), Di(Cr), Di(Mo), Di(Ni) and Di(Al), are defined as in Equation and Di(Cu) is defined as Di Cu = 1 when Cu ≤ 1 % and Di Cu = 0.36248 × % Cu + 1.0016 when 1 % < Cu, a symbol in brackets [] indicating content (mass%) of the element concerned, optionally comprising, one or more of, in mass%: B: not less than BL given by Equation below and not greater than 0.008% and Ti: 0.15% or less, (including 0%) wherein Di given by the following Equation instead of Equation is 60 or greater: Di = 5.41 × Di Si × Di Mn × Di Cr × Di Mo × Di Ni × Di Al × 1.976 where Di(Si), Di(Mn), Di(Cr), Di(Mo), Di(Ni) and Di(Al) are defined as in Equation, and wherein wherein BL = 0.0004 + 10.8 / 14 × % N − 14 / 47.9 × % Ti where ([%N] - 14 / 47.9 x [%Ti]) of less than 0 is treated as 0, a symbol in brackets [] indicating content (mass%) of the element concerned, or optionally comprising, in mass%: Cu: 0.6 to 2.0%, B: not less than BL given by Equation below and not greater than 0.008% and Ti: 0.15% or less (including 0%), wherein Di given by the following Equation instead of Equation and is 60 or greater: Di = 5.41 × Di Si × Di Mn × Di Cr × Di Mo × Di Ni × Di Al × Di Cu × 1.976 where Di(Si), Di(Mn), Di(Cr), Di(Mo), Di(Ni), Di(Al) and Di(Cu) are defined as in Equation, and wherein wherein BL = 0.0004 + 10.8 / 14 × % N − 14 / 47.9 × % Ti where ([%N] - 14 / 47.9 x [%Ti]) of less than 0 is treated as 0, a symbol in brackets [] indicating content (mass%) of the element concerned, further the forging steel optionally comprising, in mass%, V: 0.01 to 0.5% and/or optionally comprising, in mass%, one or more of: Mg: 0.0002 to 0.003%, Te: 0.0002 to 0.003%, Ca: 0.0003 to 0.003%, Zr: 0.0003 to 0.005%, and REM: 0.0003 to 0.005%, and a balance of iron and unavoidable impurities. C: 0.001 to less than 0.05%, Si: 0.7% or less, Mn: 0.01 to 4.0%, Cr: 5.0% or less, Nb: 0.005 to 0.1%, P: 0.2% or less, S: 0.35% or less, Al: 0.0001 to 2.0%, N: 0.016% or less, B: not less than BL given by Equation below and not greater than 0.008% and Ti: 0.15% or less, (including 0%) ([%N] - 14 / 47.9 x [%Ti]) of less than 0 is treated as 0, a symbol in brackets [] indicating content (mass%) of the element concerned, or Cu: 0.6 to 2.0%, B: not less than BL given by Equation below and not greater than 0.008% and Ti: 0.15% or less (including 0%), Mg: 0.0002 to 0.003%, Te: 0.0002 to 0.003%, Ca: 0.0003 to 0.003%, Zr: 0.0003 to 0.005%, and REM: 0.0003 to 0.005%, and