A resin composition contains one or more 2-methylene-1,3-dicarbonyl compounds. At least one of the one or more 2-methylene-1,3-dicarbonyl compounds has a molecular weight of 220 to 10,000, and the amount by weight of those of the 2-methylene-1,3-dicarbonyl compounds having a molecular weight of less than 220 relative the entire resin composition of 1 is 0.00 to 0.05. The 2-methylene-1,3-dicarbonyl compounds contain a structural unit represented by formula (I) below.