PURPOSE: To enable a base of a large area to be processed with a plasma by providing a plurality of downwardly open plasma generation chambers on the upper-end wall of a plasma reaction chamber, and supplying a reaction gas into each of the plasma generation chambers.

CONSTITUTION: A base support stand 3 for supporting a large base 2 is installed in the lower inside portion of a plasma reaction chamber 1 covered with a wall body, and a plurality of plasma generation chambers 5 open downward at an upper-end wall 4 are placed in the upper inside portion. A plurality of electrode blocks 8a to 8e are aligned on the upper end wall to correspond to the plural lines of plasma generation chambers 5. Gas introduced into each plasma generation chamber 5 sandwiched between alternating electrodes consisting of the array of electrode blocks 8 produces a plasma state. Therefore, large-area base processing can be carried out effectively and uniformly.