A method of manufacturing an expansion joint includes steps of: marking parts, which will form the expansion joint, on a piece of raw material, so that the original 360 degree shape of the expansion joint is equally divided by the parts, and cutting the marked parts from the raw material; welding the divided parts, so that opposing ends of the welded parts are separated from each other; bending the welded parts into the form of a cone using a bending roller, thereby welding and joining the opposing ends thereof; fixedly mounting the resultant structures on a press; shaping the mounted resultant structures into products using a mold having a desired shape and dimension; and butting a pair of the products against each other and welding the products in the outer radial direction.