PURPOSE: To obtain the high toughness spheroidal graphite cast iron casting having excellent bending deformability or the like by providing graphite-lost cavities in a decarburized layer formed at least on a part of a surface layer with a crushed shape.

CONSTITUTION: At least a part of a surface layer of a spheroidal graphite cast iron casting, i.e., the one having 0.1 to 1mm thickness is subjected to decarburizing treatment to remove graphite on the surface layer. Next, graphite decarburized cavities formed by the decarburizing treatment are crushed by the method of work hardening treatment such as shot peening treatment or rolling treatment and low temp. annealing is executed at 500 to 700°C to remove a work hardened layer formed by the above work hardening treatment. In this way, the high toughness cast iron casting having exceedingly improved safety when applied to suspension parts for an automobile which is the vital safety part requiring high bending toughness can be obtd.