To provide a thermosetting composition which enables a cured film with excellent flatness is to be formed while maintaining heat resistance possessed by a cured product of a polyesteramide acid-based thermosetting composition, and to provide a thermosetting composition with excellent low-temperature curability.

A reaction product (A) is obtained by making a dicarboxylic acid anhydride (a1), an amino compound (a2) represented by general formula (1), a hydrolyzable silicon compound (a3) other than the amino compound (a2), and a metal alkoxide (a4) react with one another.