PURPOSE: To obtain a low priced magnetron not containing an unnecessary radio wave component in its output, by connecting a folded waveguide to an output part protrusively provided to the side of an anode cylinder so as to surround the periphery of the anode cylinder and forming a band pass filter in a linear part of the waveguide.

CONSTITUTION: A cathode 21 is provided along an axial core to the inside of an anode cylinder 20, and plural vanes 22 are radially arranged surrounding said cathode, then magnetic poles 23, 24 are respectively secured to both ends of the cylinder 20. While an output part 31 is protrusively provided sideward to the cylinder 20 in the direction crossing at a right angle with a tube axis, and an antenna conductor 32 led out from one of the vanes 22 is positioned in this output part 31. Further a curved waveguide 33 is connected to the output part 31 along the periphery of the anode cylinder 20 in such a manner as to almost half surround said cylinder, and a band pass filter 34 of dumbbell shape is formed to a linear part 33a of said waveguide 33 and successively provided to an output port 36 of a mounting plate 35.