A compound capable of satisfying both high refractive index and high light resistance, and a photocurable composition containing it, are provided. Further, an optical element having good light resistance against blue laser light, and an optical head device using it, are provided.A polymerizable compound represented by SiA1A2A3A4 wherein silicon and four cyclic groups are bonded directly or via oxygen. each of A1, A2, A3 and A4 which are independent of one another, is —(O)m—X; and each of four m's which are independent of one another, is 0 or 1. X is preferably a phenyl group. From 0 to 3 hydrogen atoms in the phenyl group are substituted by a polymerizable substituent represented by CH2═CR—COO—Y—, and some or all of remaining hydrogen atoms in the phenyl group may be substituted by a methyl group or a fluorine atom.