Photopolymerizable composition

A photopolymerizable composition which comprises a polymerizable compound having at least one ethylenically unsaturated double bond and a photopolymerization initiator, wherein the photopolymerization initiator comprises an onium compound and an acridine derivative, said acridine derivative being represented by the following formula (I);

• ##STR7## wherein R.sup.1 represents an unsubstituted or substituted phenyl, alkyl or alkoxy group, and said onium compound being selected from the group consisting of compounds represented by the following formulae (II) and (III):
• ##STR8## wherein Ar.sup.1 and Ar.sup.2 may be the same or different and each represents a substituted or unsubstituted aryl group, the substituents of the aryl group being selected from the group consisting of alkyl, haloalkyl, cycloalkyl, aryl, alkoxy, nitro, carbonyl, alkoxycarbonyl, hydroxy and mercapto groups, and halogen atoms, R.sup.4, R.sup.5 and R.sup.6 may be the same or different and each represents a substituted or unsubstituted alkyl or aryl group, with the proviso that each two of R.sup.4, R.sup.5 and R.sup.6, and Ar.sup.1 and Ar.sup.2 may be bonded together through a single bond or a substituent, and X represents an anion.