Process for producing a resin having a large refractive index

1. Field of the Invention A process for producing a resin having a large refractive index which comprises curing an episulfide compound having one or more epithio structures represented by formula (1) in one molecule by polymerization in the presence of a polymerization catalyst and 0.001 to 3.0 parts by weight of a phenol derivative per 100 parts by weight of the episulfide compound. (Rrepresents a hydrocarbon group having 1 to 10 carbon atoms, R, Rand Reach represents hydrogen atom or a hydrocarbon group having 1 to 10 carbon atoms, Y represents S, O, Se or Te and m and n each represents 0 or 1).