PURPOSE: To provide an easy way of braking powder particle bridge formed at a discharging port by a method wherein valve is arranged on the upstream side of vacuum transport pipe and the pipe is temporarily closed by the valve.

CONSTITUTION: There is arranged a control means used for manually closing as required a valve 9 which is arranged on the upstream side of a transport pipe 1 in the transport pipe system and automatically closing said valve 9 by sensing a phenomenon in which vacuum pressure P in the transport pipe 1 placed near a hydraulic exhauster 2 is varied to be reduced for a long period. Thus, when the valve 9 is closed, the transport air from the air intake 4 is completely shut off, so that the vacuum pressure in the transport pipe is intensified up to the limit of the performance of the exhauster and the formed bridge is destroyed by the high differential pressure applied to the upper and lower parts of the bridge.