At an oscillation frequency of 2450 MHz band, number of the vanes constituting the
anode part of the magnetron being, the
diameter 2ra of the circle inscribing tip portions of the vanes on the
cathode side being 8.0 to 8.8 mm, the
diameter 2rc of the outer periphery of the filament constituting the
cathode part being 3.5 to 3.9 mm, the height A3 of the vane in the direction of the tube axis is 7.0 to 8.0 mm, the mutual distance A1 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 A2 between the bottom portions of the pair of pole pieces being 10.2 to 11.2 mm, the inner
diameter P1 of the through-hole of the
pole piece being 8.3 to 8.5 mm, and the outer diameter P2 of the bottom portion being 11.0 to 16.0 mm are set up.