A magnetron comprising: an anode cylinder extending cylindrically along the central axis of the magnetron extending from an input side to an output side; a plurality of vanes extending from an inner surface of the anode cylinder toward the central axis with free ends forming a vane inscribed circle; a cathode disposed along the central axis in the vane inscribed circle formed by the free ends of the plurality of vanes; an input side end hat and an output side end hat respectively fixed to the input side end and the output side end of the cathode; an input side pole piece and an output side pole piece respectively disposed at the input side end and the output side end of the anode cylinder in the central axis direction to lead magnetic flux into an electron interaction space between the free ends of the plurality of vanes and the cathode; and magnets (,) respectively disposed on the outside of the input side pole piece and the output side pole piece in the central axis direction; wherein in that when a gap between the input side end hat and output side end hat is represented by gap between end hats EHg, the length of the vane in the central axis direction by height of vane Vh, a gap between the input side end hat and the input side end of the vane by gap between input side end hat and vane IPevg, a gap between the output side end hat and the output side end of the vane by gap between output side end hat and vane OPevg, a gap between the central part of a flat surface of the input side pole piece and the input side end of the vane by gap between input side pole piece and vane IPpvg, and a gap between the central part of a flat surface of the output side pole piece and the output side end of the vane by gap between output side pole piece and vane OPpvg, a gap between the central part of a flat surface of the central input side pole piece and the central part of a flat surface of the output side pole piece is represented by PPg, conditional expressions 7.00mm≦Vh≦8.00mm 1.12≦EHg/Vh≦1.26, IPpvg> OPpvg, IPevg>OPevg and 1.35≦PPg/Vh≦1.45 are satisfied. an anode cylinder extending cylindrically along the central axis of the magnetron extending from an input side to an output side; a plurality of vanes extending from an inner surface of the anode cylinder toward the central axis with free ends forming a vane inscribed circle; a cathode disposed along the central axis in the vane inscribed circle formed by the free ends of the plurality of vanes; an input side end hat and an output side end hat respectively fixed to the input side end and the output side end of the cathode; an input side pole piece and an output side pole piece respectively disposed at the input side end and the output side end of the anode cylinder in the central axis direction to lead magnetic flux into an electron interaction space between the free ends of the plurality of vanes and the cathode; and magnets (,) respectively disposed on the outside of the input side pole piece and the output side pole piece in the central axis direction; wherein in that when a gap between the input side end hat and output side end hat is represented by gap between end hats EHg, the length of the vane in the central axis direction by height of vane Vh, a gap between the input side end hat and the input side end of the vane by gap between input side end hat and vane IPevg, a gap between the output side end hat and the output side end of the vane by gap between output side end hat and vane OPevg, a gap between the central part of a flat surface of the input side pole piece and the input side end of the vane by gap between input side pole piece and vane IPpvg, and a gap between the central part of a flat surface of the output side pole piece and the output side end of the vane by gap between output side pole piece and vane OPpvg, a gap between the central part of a flat surface of the central input side pole piece and the central part of a flat surface of the output side pole piece is represented by PPg, conditional expressions 7.00mm≦Vh≦8.00mm 1.12≦EHg/Vh≦1.26, IPpvg> OPpvg, IPevg>OPevg and 1.35≦PPg/Vh≦1.45 are satisfied.