In an ECR plasma generator, radio frequency ranging from 3 to 300 MHz is applied from a radio frequency power supply to an electrode which is provided in a chamber having an exhaust system and which serves as a shower head for gas introduction, and power is supplied to a coil provided at the outer periphery of the chamber, so as to form a magnetic field an integer number of times as large as a resonant magnetic field corresponding to the applied radio frequency, parallel with the direction of an electric field and to generate ECR plasma in an atmosphere of the supplied process gas.