A tow bar for tricycle or bicycle. By disposing the belt member 200, when a person takes a seat, it becomes possible to support the waist of sitting person since a portion corresponding to the belt member is relatively bulged out. In this exhaust gas purifying catalyst, nitrogen oxides in exhaust gas from the engine is trapped to the exhaust gas purifying catalyst when exhaust gas is in a lean region and is reduced into nitrogen by the exhaust gas purifying catalyst when exhaust gas is in a stoichiometric region or a rich region. The system further integrates the oscillator and the amplifier by inserting the amplifier cavity inside the oscillator cavity via a mirror of low reflectivity. The marks on the elastic domes represent the position with respect to the mold cavities on the mold and the parameters of fabricating the elastic membrane.