The present invention is a polymer having a polyamide structural unit, a polyamide-imide structural unit, or a polyimide structural unit, selected from a polyamide, a polyamide-imide, a polyimide, a polyimide precursor, a polybenzoxazole, and a polybenzoxazole precursor, including a reaction product of a diamine containing at least one of a diamine shown by the following general formula (1) and a diamine shown by the following general formula (2), together with at least one of a tetracarboxylic dianhydride shown by the following general formula (3) as well as a dicarboxylic acid and a dicarboxylic halide shown by the following general formula (4). This provides a polymer which is soluble in a safe organic solvent used widely, and is usable as a base resin of a positive photosensitive resin composition that is soluble in an aqueous alkaline solution and capable of forming a fine pattern to give higher resolution.