To provide a method for easily producing an air tube with a resonator without generating burr or wrinkle.

In a production method of an air tube having a resonator in a blow molding method using a split type below mold M comprising air tube main body molding parts 22, 32, communicating tube molding parts 23, 33, formed communicating with the vicinity of the center part thereof, resonator molding parts 24, 34 communicating with the air tube main body molding parts via the communicating tube molding parts, and rib molding parts 25, 35 formed at both sides of the communicating tube molding parts is used, with a parison 40 disposed on one of the cavities of the blow mold M and soft resin parts 41, 42 provided at both sides thereof fixed with the other split type auxiliary mold 27, air is blown in for the preliminarily blow molding. Afterwards, with a mold main body part 28 of the other split type mold closed, air is blown into the parison 40 for the main blow molding for forming a hard resin part 43 into a cavity shape.