PURPOSE: To provide the subject device wherein at least the upper electrode of upper and lower parallel electrodes is finely divided, thereby to facilitate observation of plasma and samples, and optical detection thereof.

CONSTITUTION: The upper electrode of the upper and lower parallel electrodes is formed by strip-shaped upper electrodes 11a through 11c and a short-circuiting rod 11' which are divided finely. A smaple is disposed on a dielectric plate 14 and a gas plasma is generated between delectric plates 12 and 14 to carry out etching. Upon this occasion, the detection between the upper electrodes 11a through 11c of the variation in the intensity distribution of emission specturm of plasma, observation of etching conditions, and light ray irradition from the outside, can be effected without being disturbed by plasma. Accordingly, excitation of plasma, and heating of samples can be carried out effectively