The water gas shift reactor includes a gas reaction tank including a reaction chamber formed in the shape of a hollow body provided with a porous plate installed therein to divide the inside of the reaction chamber into an upper reaction space and a lower collection space and a catalyst stacked on the upper surface of the porous plate to convert carbon monoxide into hydrogen, and an insulating layer provided at the outer surface of the reaction chamber, a syngas storage tank to store the syngas, a syngas supply pipe to supply the syngas to the gas reaction tank, after the syngas is heated by a preheater, a steam supply pipe to supply steam generated from a steam generator to the gas reaction tank such that the steam reacts with the syngas, after the steam is heated by a preheater, and a reaction gas discharge pipe.