To exhaust pumping a large volume of gas or even the lowest plasma discharge potential with effective cost by providing at least two connected individual exhausting means and by exhausting a reactor until a middle pressure by a first exhausting means of a reactor and at least until plasma discharging potential by a final exhausting means.

At first a container 1 standing on a bottom 20 of a reactor 6 is pushed into a chamber 5, and the bottom 20 is pushed compressing to an external electrode 10 to close the chamber 5 with an intermediating seal. Then an interior space of the chamber 5 is exhausted at an exhausting device 7 together with that of the container 1, that is, until a standard of plasma discharging potential. A processing gas is supplied from a supplying line 17 positioned at an inside of an internal electrode 11, and rest air is substituted from downward to upward from the container 1 to suck out to a head area of the reactor 6. In this case, three exhausting stages that are connected but are individual are provided. Decompression chambers 26, 27 disposed at each exhausting stage and pumps 32, 33, 34, respectively belonging to the chambers are not operated in series, however are connected in parallel to achieve a large pressure difference at multistage exhaust.