The present invention relates to a resin solution composition containing at least one resin selected from the group consisting of aromatic polysulfones, aromatic polyamideimides, aromatic polyetherimides, aromatic polyimides and aromatic polyamic acids, a sulfone-based solvent, and an ester-based solvent, wherein in this resin solution composition, an amount of the resin, relative to the total mass of the resin solution composition, is at least 10% by mass but not more than 50% by mass, and an amount of the ester-based solvent, relative to the total amount of the sulfone-based solvent and the ester-based solvent, is at least 15% by mass but not more than 85% by mass.