A low dielectric constant, a low dielectric loss tangent, and heat resistance are achieved. An active ester resin that has a resin structure produced by reacting a polyfunctional phenolic compound (a1) with a monofunctional aromatic carboxylic acid or its chloride (a2) and an aromatic dicarboxylic acid or its chloride (a3). The polyfunctional phenolic compound (a1) is represented by structural formula (1) below: (where Ar represents a benzene ring, a naphthalene ring, a benzene ring nuclear-substituted by an alkyl group having 1 to 4 carbon atoms, or a naphthalene ring nuclear-substituted by an alkyl group having 1 to 4 carbon atoms, X represents a methylene group, a divalent cyclic aliphatic hydrocarbon group, a phenylene dimethylene group, or a biphenylene-dimethylene group, and n represents the number of repeating units and the average thereof is in a range of 0.5 to 10).