An object is to provide a resin composition having excellent performance as a binder such as adhesiveness and, at the same time, retaining solution properties favorably even after a solution is stored for a long period of time. A modified polyolefin resin composition includes a modified polyolefin resin (C), in which the modified polyolefin resin (C) is a resin made by modifying a polymer (A) that is a polymer (a) of a polyolefin resin or a chlorinated polyolefin resin and an α,β-unsaturated carboxylic acid derivative having a structure derived from at least one carboxy group or a chlorinated product (b) thereof with a modification component including an alcohol (B); and a residual ratio of the structure derived from at least one carboxy group in the modified polyolefin resin (C) is 50% or more and 80% or less.