To provide a plug apparatus mounted to a spray machine or a pneumatic transport apparatus, in which stable transport state can be continued, and safe and stable work can be performed.

Air pulses are generated at regular intervals in a material tank and/or a transport circuit and/or a plug forming space portion (plug nozzle) disposed in an intermediate portion between them, a material plug or an air plug is formed by the air pulses, and the lengths of material plug and the air plug can be arbitrarily changed by a control apparatus.