To provide a magnetron improved in high efficiency and load stability while suppressing costs. By shortening the height of vane Vh so that the ratio of the height of vane Vh to a gap between end hats EHg (EHg/Vh) satisfies a condition 1.12≦EHg/Vh≦1.26, an input side pole piece-vane gap IPpvg becomes larger than an output side pole piece-vane gap OPpvg, and an input side end hat-vane gap IPevg becomes larger than an output side end hat-vane gap OPevg, load stability at high efficiency can be improved while shortening the height of vane Vh. Therefore, it is possible to provide a magnetron improved in high efficiency and load stability while suppressing costs.