Crosslinked polyimide compound and use thereof

[Object] To provide a polyimide compound which can be dissolved in a certain solvent and has high molecular weight, and a preparation process thereof which produces the compound by industrially advantageous process. [Solving Means] A polyimide compound crosslinked with a polyamine which is soluble in the specific solvent is produced by dehydration and condensation of amino acid or salt thereof and polyamine in an organic solvent under the presence of protonic acid. In particular, in the case of using a polyamine having low solubility to an organic solvent such as especially lysine, ornithine, etc., reaction rate of the polymerization can be increased by adding a polyamine in the step before or initial polymerization because water which is contained in the raw material or produced in the dehydration reaction saves as a good solvent for the polyamine.