PURPOSE: To generate highly efficient/highly dense plasma in a microwave plasma processing device to transform processing gas into the plasma by using an electronic cyclotron resonance phenomenon caused by a correlation of an electric field generated by means of a microwave with a magnetic field orthogonal to this electric field.

CONSTITUTION: Circumferential length in a single turn of a spiral shape antenna 1 is set approximately equal to a wave length of a microwave, and a pitch interval is set to become length of 0.1-0.5 times the wave length of the microwave. In order to radiate the microwave only in one axial direction, a metallic plate 2 is provided. In this case, an angle between the metallic plate 2 and a metallic wire of the antenna 1 is set between 12°-18°. The spiral direction is set in a clockwise direction toward the radiating direction.