An improvement of a high density pneumatic transport system for pneumatically transporting powdered or granular materials placed in an airtight storage container to a collector through a transport pipe having a vertical riser pipe intermediately thereof by the use of pressurized gas. The transport pipe comprises a lower horizontal pipe being connected to the airtight storage container and having a convergent cylindrical accelerating reducer, an upper horizontal pipe being connected to the collector and having a divergent cylindrical decelerating reducer at its initial end, and a vertical riser pipe which connects the lower horizontal pipe to the upper horizontal pipe. The vertical riser pipe is provided at intermediate thereof up and down with an acceleration regulating reducer having a convergent accelerating portion above its bottom having a constricted portion and a divergent cylindrical decelerating reducer.