A magnetron has an anode cylinder, ten vanes, three strap rings. The ten vanes are fixed to an inner surface of the anode cylinder and arranged in a radial pattern of which center is at an axis of the anode cylinder. Each of the three strap rings connects vanes that are alternatively arranged. A first strap ring and a third strap ring are arranged on a first end of the vanes in a direction of axis, and a second strap ring is arranged on a second end that is opposite to the first end. Outer diameter of the second strap ring is equal to inner diameter of the first strap ring and outer diameter of the third strap ring is equal to inner diameter of the second strap ring.