The present invention discloses a processed air supply apparatus, air pressure in a pipeline downstream of which is remained below atmosphere pressure, and optimum processed air is supplied corresponding to FPD cardinal plate procession. A supplier (400) supplies processed air to an upper electrode (300), and a buffering chamber (330) in the upper electrode separates a central chamber with perimeter chamber; the processed air supply apparatus is provided with branched pipe (404, 406) that shunts processed air from an air box (410) in two; and a flow adjustment unit (420, 430) that adjusts flowthat flows over these branched pipes, and imports the processed air in each branched pipe into the central chamber and the perimeter chamber; each flow adjustment unit is provided with switch valve (422, 432) and fixed throttling controller (424, 434) that set on each branched pipe; the flow adjustment unit connected with the central chamber branched pipe is provided with a bypass pipe (404A) that parallel to the switch valve and the fixed throttling controller, at the same time the bypass pipe is provided with a switch valve (422A).