Magnetron is provided to reduce the length of the filter device along the axial direction of cathode by installing the upper insulation part at the upper part of the choke coil. An anode(131) forms the cavity resonator while being arranged inside a yoke(111). A cathode(151) emits the thermoelectron reaching to the anode. A main body(110) comprises an insulator(127) protruded from the bottom of yoke and produces and outputs the high frequency energy. A choke coil(165) is nearly arranged to the yoke more than the bottom surface of insulator. A filter box(161) is arranged at the bottom side of yoke in order to contain the insulator and choke coil inside. A upper insulation part(171) is arranged so that the insulating distance of the choke coil and the bottom side of yoke is extended.
