There is provided novel thermosetting resin composition. A thermosetting resin composition comprising a polymer having at least one structural unit of the following Formula (1): {wherein each of R1 and R2 is independently a hydrogen atom or a C1-4 alkyl group, X is a single bond or a divalent organic group, and Y is an arylene group of the following Formula (2): (wherein Z1 is a carbonyl group or a —CONH— group, Z2 is a C1-5 alkylene group or a 5- or 6-membered divalent saturated heterocyclic group containing at least one nitrogen atom, and Z3 is a 5- or 6-membered aromatic heterocyclic group containing two nitrogen atoms in which at least one of hydrogen atoms may be substituted by a C1-5 alkyl group)}.