1. A partially imidized polyamic acid composition comprising: a conductive carbon black; and a partially imidized polyamic acid obtained by a polymerization and imidization reaction of a diamine compound, a tetracarboxylic acid dianhydride, and an acid monoanhydride at a quantitative ratio satisfying the following Relational Expression (1) and Relational Expression (2): 
 0.962 ≦Y/X ≦0.997  Relational Expression (1) 
 0.20 ≦Z /2( X−Y )<0.80  Relational Expression (2) wherein, in Relational Expressions (1) and (2), X represents a content by mol of the diamine compound, Y represents a content by mol of the tetracarboxylic acid dianhydride, and Z represents a content by mol of the acid monoanhydride, the partially imidized polyamic acid has an imidization ratio of from 4.1% to 25.0%, and a main molecular skeleton of the polyamic acid is represented by the following Formula (1): wherein: R is selected from any one of the following divalent aromatic residues: R′ represents a tetravalent aromatic residue or a tetravalent aliphatic residue, n represents a positive number, and R″ represents a terminal of a molecule and is selected from hydrogen or an organic group formed by the acid monoanhydride.