1. A polyamic acid composition comprising: a conductive carbon black; and a polyamic acid in which a diamine compound, a tetracarboxylic acid dianhydride, and an acid monoanhydride have been reacted 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.