PURPOSE: To obtain high-density plasma with high efficiency and to obtain a small-sized and inexpensive electric discharge device by generating standing waves in the plasma.

CONSTITUTION: A gas for electric discharge is introduced into a cylinder 10 consisting of a high melting insulating material in a plasma generating part 1. DC voltage is passed to a coil 13 to form a magnetic field B in an arrow direction. An antenna 14 is provided along the cylinder 10 and a high-frequency voltage is impressed from a high-frequency power source 15 thereto to apply the high-frequency alternating magnetic fields to the inside of the cylinder 10 in the direction intersecting orthogonally with the magnetic field. The standing waves are formed in the plasma if the gaseous pressure in the cylinder 10 is set at a prescribed value and the high frequency and the magnetic field are set in a certain specific relation. The high density plasma is extremely efficiently obtd. with the high-frequency power source of a small capacity under such conditions. The resulted plasma is introduced into a treatment chamber 20 and the surface treatment of a substrate 24 is executed.