A resin composition includes: (A) a polymer having a structural unit shown by the formula (I), and an acidic functional group or a group derived therefrom at both of the terminals; wherein X1 is a di- to octa-valent organic group, Y1 is a di- to octa-valent organic group, R1 is a hydrogen atom or an organic group having 1 to 20 carbon atoms, R2 is a hydrogen atom or a monovalent organic group, when plural R1s or R2s exist, the plural R1s or R2s may be the same or different, p and q are independently an integer of 0 to 4, l and m are independently an integer of 0 to 2, and n is an integer of 2 or more indicating the number of structural units; (B) a solvent; and (C) a compound shown by formula (II) wherein R3 is a monovalent organic group.