NOVELTY - A polyisoimide resin contains benzofuran-type repeating unit(s) (I)-(III), and has melting point of 300 degrees C or less measured by differential scanning calorimetry. The transition temperature of polyisoimide resin is higher than its melting point, measured by differential scanning calorimetry.    USE - Polyisoimide resin is used for manufacturing polyimide resin used as transparent heat resisting material for manufacturing polyimide resin molded product (all claimed) e.g. film, sheet, molding material and coating. Uses include but are not limited to flexible solar cell, integrated circuit packaging tray, tray for integrated circuit manufacturing process, liquid crystal display carrier, gear for copier, bearing retainer, high-density magnetic-recording base, oil seal ring, piston ring, slide bush for stretch machine, heat-resistant insulating tape, and bobbin of structural component.    ADVANTAGE - The polyisoimide resin has excellent solubility with respect to solvent, and thermoplasticity. The polyimide resin molded product formed using polyisoimide resin has excellent heat resistance and transparency.    DETAILED DESCRIPTION - A polyisoimide resin contains benzofuran-type repeating unit(s) of formulae (I)-(III), and has melting point of 300 degrees C or less measured by differential scanning calorimetry. The transition temperature of polyisoimide resin is higher than its melting point, measured by differential scanning calorimetry.    R1=group of formula (iv);    ring A, ring B=aliphatic ring or aromatic ring (both optionally substituted);    p,q=1-10;    X=single bond, O, S, optionally substituted alkylene, sulfonyl, sulfide, carbonyl, aromatic group or -O-CnH2n-O-;    n=1-5;and    Y1,Y2=single bond, O, S, optionally substituted alkylene, sulfonyl or sulfide.    INDEPENDENT CLAIMS are included for the following:    (1) manufacture of polyimide resin molded product, which involves rearranging polyisoimide resin;    (2) manufacture of polyimide resin molded product, which involves coating a solution containing polyamic-acid resin or polyamic acid ester resin, molding, cyclizing obtained molded product, and rearranging polyisoimide resin of obtained polyisoimide resin molded product; and    (3) manufacture of polyisoimide resin, which involves performing cyclization of polyamic acid resin or polyamic acid ester resin containing benzofuran-type repeating unit(s) of formula (IV)-(VI).    R2=1-14C optionally substituted alkyl or H.