The invention provides a process for the production of polyisocyanate which permits effective utilization of hydrogen chloride formed in the production of polyisocyanate as a by-product and reduction in environment load, and equipment for realizing the process. Carbonyl chloride is formed in a reaction tank (2) for the production of carbonyl chloride by reacting chlorine with carbon monoxide, andthen reacted with polyamine in an isocyanation tank (3) to form a polyisocyanate. Hydrogen chloride gas formed as a by-product in the tank (3) is purified in a hydrogen chloride purification column (4) and then oxidized in a hydrogen chloride oxidation tank (6) into chlorine. This chlorine is fed into the tank (2) through a chlorine recycling line (8) and reacted with carbon monoxide to form carbonyl chloride.