PURPOSE: To attain the prevention of explosion by constituting the titled powdery substance treatment device so that the powdery substance is sucked and dispersed in a surfactant and interrupted from air while gas is passed through the surfactant layer which is provided to a gas suction route in a closed state from the inside of a reaction vessel.

CONSTITUTION: An a-Si film is formed on an electricall-conductive supporter 12 by introducing a reaction gas contg. Si and gaseous N2 into a reaction vessel 11 of a plasma CVD device 10. The exhaust gas contg. the powdery substance essentially composed of polysilane generated in the inside of the vessel 1 during this period is sucked 27 into the inside of a suction vessel 22. Then while this exhaust gas is permeated through a mesh plate 26 formed with a membrane of a purifying agent 24, the powdery substance is dispersed in the purifying agent and treated. Also during the treatment of the powdery material, the purifying agent 24 is successively conducted 34 to a separation vessel 36 from the vessel 22 and the powdery substance having positive electric charge is adsorbed on an electrode 37b, separated and broken off together with the paper of the surface of the electrode 37b and incinerated or discard- treated. On the other hand, the purifying agent 24 free from the powdery substance is returned to the inside of the vessel 22 in order to redisperse the powder substance 1. Further since the powdery substance separated from the electrode 37b is covered with the low-volatility purifying agent 24 and interrupted from air, the probability of explosion is not caused.