Disclosed is a method for the quantitative analysis of a metal element contained in a resin material, which permits quantitatively analyzing the harmful substance such as lead contained in a resin material, comprising decomposing the resin material within a container having at least the inner surface formed of a glassy carbon in the presence of an aqueous solution of an oxidizing acid, heating the organic residue of the decomposed resin material so as to convert the residue into an ash, and quantitatively measuring the metal element contained in the organic residue converted into the ash.