To provide a magnetron of a microwave oven improving the quality and efficiency of the oscillated frequency by rising a Q value without changing the frequency but by changing a geometric structure of large and small strip rings.

This magnetron comprises a positive electrode cylinder, a plurality of vanes configurating a positive electrode part with the positive electrode cylinder, and the large strip ring and the small strip ring respectively mounted on upper parts and lower parts of the vanes and electrically connected to the vanes. The large strip ring has an inner diameter of 17.1-18.01 mm, and an outer diameter of 18.6-19.6 mm, and the small strip ring has an inner diameter of 13.4-14.4 mm, and an outer diameter of 14.9-15.9 mm. The large and small strip rings respectively have a height of 1.55-1.65 mm, and a distance between the inner diameter of the large strip ring and the outer diameter of the small strip ring is kept within an error range of 2.20 mm.