To improve material strengths of a roadbed material obtained by using steel-making slag and suppress elution of fluorine from the roadbed material.

The roadbed material 4 is obtained by mixing hardened cement 2, obtained by hardening cement paste 1 prepared by kneading cement and water, with steel-making slag 3, and then crushing and sizing the resulting mixture so that the average particle diameter becomes ≤50 mm. Accordingly, it becomes possible to use the steel-making slag in wide applications although the steel-making slag has limited uses because of low strength and elution of fluorine.