A magnetron includes a cooling block (10) having an annular continuous portion with opposite end portions (12a, 12b) opposed to each other, the cooling block being secured to an outer peripheral surface of the cylindrical anode body, the cooling block having a coolant circulation pathway defined therein, a tightening member (15) engageable with the opposite end portions of the cooling block to tighten the cooling block by reducing a distance between the opposite end portions of the cooling block, and a pair of pipe joints (14) each connected to a portion of the cooling block adjacent to one of the opposite end portions so as to communicate with the coolant circulation pathway. The tightening member is disposed between connecting portions of the pair of pipe joints with the cooling block so as to extend in a direction inclined with respect to a plane including an annular direction of the cooling block.