Abstract: An exhaust gas recycling device for use in reducing the nitrogen oxide (NO.sub.x) concentration of exhaust gases from gasoline engines has between two metal plates superposed on each other a main channel defined by a first inflated portion of large cross section, and at least one branch channel defined by a second inflated portion communicating with the main channel and having a small cross section. The device comprises a single component provided by two metal plates, and is simple in construction and reduced in the number of parts, manufacturing cost and weight. The device is produced by roll-bonding two metal plates, forming at least one second inflated portion having a small cross section and defining the branch channel by primary inflation with a low fluid pressure, thereafter holding the two metal plates with dies, and forming a first inflated portion having a large cross section and defining the main channel by secondary inflation with a high fluid pressure.