To increase the yield of products by suppressing polymerization shrinkage to prevent the occurrence of recesses of lenses, in consideration of the fact that it is required to prevent the occurrence of defects due to recesses of lenses caused by polymerization shrinkage during polymerization, of a stock solution of polymerization where a hydrophilic component is monomer and a hydrophobic component is copolymer.

In a method for manufacturing a soft contact lens, a stock solution including a polymer containing a methacrylate ester as a monomer and a hydrophilic monomer having a polymerizable group is thermally polymerized, and the sum total of heating temperatures for four hours after the start of heating is 130°C h or more and 150°C h or less, and polymerization shrinkage after polymerization does not occur to prevent appearance defects. By this invention, the occurrence rate of defects due to recesses of lenses is 0%, and the yield of products can be increased.