2-Arylnaphtho[1,8-bc]furan-5-ones represented by general formula (I): ##STR1## wherein G represents a substituted phenyl group, an unsubstituted or substituted 1-naphthyl group and an unsubstituted or substituted 2-naphthyl group, with the substituents being selected from the group consisting of a straight chain or branched chain alkyl group having 1 to 5 carbon atoms, a straight chain or branched chain alkoxy group having 1 to 3 carbon atoms and a halogen atom; are disclosed as well as photopolymerizable compositions containing at least one of the above compounds as a photopolymerization initiator for addition polymerizable ethylenically unsaturated compounds.