PURPOSE: To obtain a composition, comprising an ethylenically unsaturated compound, an acylphosphine oxide compound, a specific photopolymerization initiator and an organophosphine compound, sensitive to visible light with a high sensitivity and good in polymerization rate.

CONSTITUTION: The composition is obtained by blending (A) an ethylenically unsaturated compound with (B) an acylphosphine oxide compound, (C) a photopolymerization initiator expressed by the formula (R1 and R4 are alkyl; R2, R5 and R6 are H or alkyl; R3 is alkylene; m is 0-4; n is 0-5) and (D) an organophosphine compound as essential components. An aliphatic acrylate, an aromatic acrylate, etc., are used as the component (A) and 2-hydroxy-2- methyl-1-phenylpropan-1-one, etc., are preferred as the component (C).