The present invention is to provide an apparatus and a method for generating an electron beam. The apparatus for generating an electron beam includes a housing and a first waveguide. A resonance cavity is prepared in the housing. The first waveguide is combined with the outer circumference of the housing and connected to the resonance cavity through a first coupling hole. The first coupling hole is prepared in the sidewall of the first waveguide. An electromagnetic wave is applied to the bottom of the first waveguide. The electromagnetic wave reaches the housing through the first waveguide.
