TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Property: The purity as measured by gas chromatography analysis of the solvent used for manufacturing the copolyimide precursor is 99.8% or more.    TECHNOLOGY FOCUS - POLYMERS - Preferred Composition: The ratio of number of units (I) and number of units (II) is 50/50-99.5/0.5. The ratio of number of units (III) and number of units (IV) is 50/50-99.5/0.5. The diamine component does not contain aromatic diamine (derivative) having a light transmittance of 90% or more, but contains an aromatic diamine (derivative) having a light transmittance of 80% or more. The transmittance of diamine component is at a wavelength of 400 nm with respect to a solution obtained by dissolving in pure water or N,N-dimethylacetamide in a concentration of 10 %mass at an optical path length of 1 cm. The tetracarboxylic-acid component contains tetracarboxylic acid (derivative) having a light transmittance of 75% or more. The transmittance is at a wavelength of 400 nm with respect to a solution obtained by dissolving in 2N sodium hydroxide solution in a concentration of 10 %mass at an optical path length of 1 cm. The diamine not having an aromatic ring with respect to the total molar quantity of diamine component is contained in an amount of 50 mol% or more, and the content of aromatic diamine is 50 mol% or more. Preferred Properties: The logarithmic viscosity in 0.5 dL/g N,N-dimethylacetamide solution at 30 degrees C of the copolyimide precursor is 0.2 dL/g or more. The breaking elongation at room temperature when a film of thickness 10 mu m is formed using the copolyimide is 8% or more, preferably 10% or more, the light transmittance at 400 nm is 50% or more, preferably 75% or more, the elasticity modulus at room temperature is 3 GPa or more, and the average linear thermal expansion coefficient at 50-200 degrees C is 20 ppm/K or less. In a dynamic-viscoelasticity measurement, the film has a maximum storage elastic modulus compared with the minimum storage elastic modulus on the glass transition temperature calculated from the maximum point of tan- delta above the temperature of minimum value. The transmittance at a wavelength of 400 nm with respect to a solution obtained by dissolving the polyimide precursor in a polar solvent in a concentration of 10 %mass at an optical path length of 1 cm is 90% or more. Preferred Definitions:    X=tetravalent group chosen from groups of formulae (iii)-(x).