To provide a steel in which P therein is made harmless to a level which has not been achieved heretofore by dispersing the segregation of P inside the steel only by the addition of Nd.

The steel contains, by mass, 0.10 to 0.30% C and 0.005 to 0.030% P, and has a ferritic phase as a solidified primary crystal, and completes the solidification in an austenitic phase at a solidus temperature, wherein Nd is added in an amount to satisfy the relationship of 2.510-4/[P][Nd]3.510-3/[P] in accordance with the concentration of P, and further, in an amount to satisfy the relationship of 6([O]+[S])+1.610-4/[P][Nd]6([O]+[S])+2.710-3/[P] in accordance with the concentrations of P, O and S when the steel further contains 0.005% O and 0.005% S, thus the microsegregation of P is dispersed.