The present invention provides a resin composition which can be cured by visible light and whose cured product is not colored or little colored, said composition comprising a phosphine oxide compound represented by the following general formula (1) (wherein R.sup.1 represents alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, substituted or unsubstituted aryl, substituted or unsubstituted heteroaryl, substituted or unsubstituted aralkyl, or substituted or unsubstituted aralkenyl; and R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8 and R.sup.9, which may be the same or different, each represent a hydrogen atom, a halogen atom, alkyl, alkenyl, substituted or unsubstituted aralkyl, or substituted or unsubstituted aralkenyl, and two adjacent groups among R.sup.2, R.sup.3, R.sup.4, R.sup.5, R.sup.6, R.sup.7, R.sup.8 and R.sup.9 may form a hydrocarbon ring together with the two carbon atoms adjacent thereto) and an unsaturated compound. ##STR00001##