PURPOSE: To provide a cast iron graphitizing method capable of shortening treatment time and improving mechanical properties at the time of graphitizing cast iron, particularly graphitizing the white pig iron structure of a malleable cast iron casting.

CONSTITUTION: At the time of graphitizing cast iron which has a composition containing, by weight, 1.0-4.5% Si and ≥2.0% C and satisfying 3.0%≤C+1/3Si≤4.5% and also has a white pig iron structure, heating temp. is regulated to 900-1050°C and also temp. is raised so that heating velocity becomes ≤60sec by temp. rise time up to 900°C, followed by tempering. In the graphitization method for cast iron, after temp. rise up to heating temp., holding time at this temp. is regulated so that it is shorter than the length of time necessary to graphitize cast iron homogeneously as far as the inner part of the material.