At an oscillation frequency of 2450 MHz band, number of the vanes constituting the
anode part of the magnetron being, the
diameter 2 ra of the circle inscribing tip portions of the vanes on the
cathode side being 8.0 to 8.8 mm, the
diameter 2 rc of the outer periphery of the filament constituting the
cathode part being 3.5 to 3.9 mm, the height A 3 of the vane in the direction of the tube axis is 7.0 to 8.0 mm, the mutual distance A 1 between the bases of the pair of funnel-shaped pole pieces fixed to both sides of the
anode part being 21.5 to 23.5 mm, the mutual distance A 2 between the bottom portions of the pair of pole pieces being 10.2 to 11.2 mm, the inner
diameter P 1 of the through-hole of the
pole piece being 8.3 to 8.5 mm, and the outer diameter P 2 of the bottom portion being 11.0 to 16.0 mm are set up.