To provide an operation method of a powder and granular material supply device capable of preventing an exposure and pollution, by exhibiting the high cleaning effect, by using a device of a simple constitution.

This operation method of the powder and granular material supply device 10 comprises a first connecting pipe 12 and a second connecting pipe 24, and is formed so that the first connecting pipe 12 is provided with a first butterfly valve 14, and the second connecting pipe 24 is provided with a second butterfly valve 34, respectively, and a cleaning nozzle 26 is arranged between the two butterfly valves, and comprises a docking process of connecting the first connecting pipe 12 and the second connecting pipe 24, a powder and granular material supply process of opening a valve in order of the second butterfly valve 34 and the first butterfly valve 14, a first air blow process of jetting air from the cleaning nozzle 26 by blocking up the first butterfly valve 14, a cleaning process of injecting a cleaning liquid from the cleaning nozzle 26 by blocking up the second butterfly valve 34, and a second air blow process of jetting the air from the cleaning nozzle 26.