A variable frequency microwave pulse generator that includes a high voltage charger for charging with a high voltage, a high pressure gas tank for supplying insulation gas, and an electrode discharge unit. The electrode discharge unit includes a case, an accommodation section defined inside the case, and a pair of electrode sections disposed at one side and the other side of the accommodation section so as to face each other. The pair of electrode sections is spaced apart from each other to define a spark gap therebetween where the insulation gas supplied from the high pressure gas tank is loaded. An annular resonance recess is defined at the central portion of one electrode section of the pair of electrode sections, the depth of the resonance recess being variable in response to an adjustment knob disposed on the case being manipulated.