<p>A magnetron in accordance with the present invention is configured so that an antenna lead (17) connected to a desired position of an anode segment (2) passes through a magnetic pole piece (7) and a metal cylinder (8) so as not to make contact therewith and is connected to the output portion (20) of the magnetron, and so that the electrical length L1 of this antenna lead (17) between the opening end of a third harmonic restraint choke (15) and the connection portion of the anode segment (2) is 1/2 of the wavelength (») of the third harmonic, thereby restraining the third harmonic and the side bands of the third harmonic.</p>
