Carburizing steel having excellent cold forgeability, and production method thereof

The present invention provides a carburizing steel which has a composition that contains, in terms of mass percentages, 0.1 to 0.35% of C, 0.01 to 0.22% of Si, 0.3 to 1.5% of Mn, 1.35 to 3.0% of Cr, 0.018% or less of P, 0.02% or less of S, 0.015 to 0.05% of Al, 0.008 to 0.015% of N and 0.0015% or less of O within ranges that satisfy formulae (1), (2) and (3), with the remainder comprising Fe and unavoidable impurities, and in which the total structural fraction of ferrite and pearlite in the steel structure is 85% or higher and the average ferrite particle diameter is 25 [mu]m or lower. 3.1>=[([%Si]/2) + [%Mn] + [%Cr]]>=2.2 --- (1), [%C] - ([%Si]/2) + ([%Mn]/5) + 2[%Cr]>=3.0 --- (2), 2.5>=[%Al] / [%N]>=1.7 --- (3), wherein [%M] denotes the content (mass%) of an element M.