An ion source is provided. The ion source includes a plasma generation container, an electron supply, an electromagnet and a shift means. The plasma generation container generates an ion beam to be extracted therefrom in an ion beam extraction direction. The electron supply supplies electrons into the plasma generation container. The electromagnet generates a magnetic field for capturing the electrons from the electron supply. The shift means shifts a center of the magnetic field in the ion beam extraction direction to change a rate of a desired type of ion to be contained in the ion beam.