To provide a polyimide-based heat-resistive resin composition capable of forming a coated film and a seamless pipe body excellent in tear strength and elongation.

A polyimide resin is obtained by reacting an aromatic diamine and an aromatic tetracarboxylic dianhydride, wherein the aromatic diamine contains ≥5 eq% of 2,3'-diaminodiphenyl ether represented by the following structural formula based on the whole aromatic diamine amount; and a coated film composed of the polyimide resin has a tear strength at 23°C of ≥5 N/mm, and a tensile elongation at 23°C of ≥50%.