A polyamic acid according to one or more embodiments of the present invention contains a structural unit represented by general formula (1) and a structural unit represented by general formula (2). In general formula (1), the plurality of R1s are each independently a hydrogen atom, a monovalent aliphatic group or an aromatic group. In general formula (2), the plurality of R2s are each independently an alkyl group having 1-3 carbon atoms or an aryl group having 6-10 carbon atoms. In general formulas (1) and (2), X is a tetravalent organic group. In general formula (2), the plurality of Ys are each independently an alkylene group having 1-3 carbon atoms or an arylene group having 6-10 carbon atoms, and m is an integer of 51-199.