PROBLEM TO BE SOLVED: To provide a method and device for generating a new short-pulse microwave capable of simply obtaining a short-pulse microwave.
SOLUTION: A continuous or long-pulse microwave oscillated from a microwave oscillator 1 is propagated to a waveguide 2 filled with specified gas. Next, a laser beam of prescribed intensity is irradiated from a laser beam source 4 to the parts A and B of the waveguide 2 to partially make the prescribed gas plasma. Then, the microwave cannot pass through the part of the specified gas, which is made to be plasma, and it is reflected. Then, the microwave is cut off at the part, thereby the pulse of the microwave is shortened.