A polymerizable composition containing: (A) a polyurethane compound soluble or swellable in water or an aqueous alkali solution which is obtained by reacting at least one diol compound having an unsaturated bond in a main chain and having a molecular weight of 500 or more with at least one polyisocyanate compound; (B) a radical initiator; and (C) a photothermal converting agent, and a polymerizable composition containing: (A') a polyurethane resin which is soluble or swellable in water or an aqueous alkali solution and has an unsaturated carbon-carbon bond in its side chain; and (B) a radical initiator, wherein the polyurethane resin (A') is obtained by adding an epoxy compound having an unsaturated carbon-carbon bond to a polyurethane resin having carboxyl group.