In a surface treatment apparatus (30) of the face type, a porous dielectric (37) is supported by the outer periphery portion of the supporting member (45) under the bottom surface of a porous electrode (32). The dielectric can be supported by the supporting member to permit the thermal expansion deformation of the dielectric by forming an upward inclined-face (47) and a downward inclined-face (43) on the supporting member (45) and the dielectric (37), respectively. Further, a discharge gas can be supplied uniformly to a discharge region (51) through the electrode (32) and the dielectric (37), both of which are porous. Many gas exhaust ports (41), by which the flow rate of the gas can be regulated, are provided around the discharge region (51). Thus, the gas is uniformly exhausted around the discharge region (51). Especially, if the gap between the dielectric (37) and a work (39) depends on mounting accuracy or the like and varies with location, the gas can be exhausted uniformly around the discharge region (51).