A gas shower head having many gas discharging ports formed on the lower surface is provided on the top wall of a processing container such that the gas shower head faces a placing table on which a substrate is to be placed, and the top wall of the processing container at the periphery of the gas shower head is composed of a dielectric material. A coil is provided on the dielectric material, and the phase of high frequency waves to be supplied to the gas shower head and the coil is adjusted so that the phase of the electrical field in a processing region above the substrate and the phase of the electrical field in the peripheral region surrounding the processing region are same or opposite to each other.