PURPOSE: To integrally simplify the holding structure of a plurality of blade- shaped electrodes by juxtaposing a plurality of slits with a flat-plate electrode substrate excepting a surrounding frame body of insulating material corrosive resistant to a reaction gas and by arranging the blade-shaped electrodes between the slits.

CONSTITUTION: A plurality of slits 3,... are transversely juxtaposed with a flat-plate electrode substrate 1 excepting a surrounding frame body 2 of insulating material such as ceramic corrosive resistant to a reaction gas and strip-like blade-shaped electrode substrates 11 are arranged between respective slits 3, 3. Also, a guide groove 12 is formed in the central part of the width of the tip edge of each blade-shaped electrode substrate 11 and in the frame body 2, 2 continuing from the central part and a conductive wire electrode 13 is caused to run along the guide groove 12. Thus, blade-shaped electrodes are integrated with the surrounding frame body, the frame body operates as reinforcing material and the frame body exists around the blade-shaped electrodes so that an atmospheric gas containing the reaction gas can be supplied into the frame body.