To obtain a compsn. which is highly sensitive to light and, when given light and/or heat energy, gives a cured item having good characteristics by using a base generator having a specified structure and a sensitizer as a polymn. initiator for a base-curable compd. and a free-radical polymerizable compd.

The base generator is represented by the formula: LnRu3+.3BAr3 R- (wherein L is a ligand selected from among ammonia, pyridine, imidazole, ethylenediamine, etc.; n is the coordination number of L and is an integer of 2-6; Ar is a 6-18C monocyclic or fused polycyclic aryl group optionally substd. by fluorine, etc.; and R is a 1-18C alkyl group optionally substd. by fluorine, etc.). Hexaammineruthenium (III) complex ion is an example of the Ru (III) complex ion, and triphenylmethyl borate is an example of the borate anion. Anthracene derivs. (e.g. anthracene) are listed as the sensitizer.