PURPOSE: To reduce the air flow pressure of a cooling blower by providing cuts covering from the ends of heat radiation blade to the positions near the external surface of the main unit of a magnetron and bending the ends of the heat radiation blade in steps possessing their own gradients mutually opposite to each other.

CONSTITUTION: A penetrating hole 10 for press-in engagement is provided in the central area 8 by forming a burring area 9 adhering to the external surface of the main unit of a magnetron. Cuts 11 and 12 which approach to the external surface 4 from both right and left ends are provided. In the figure partitioned by the cuts 11 and 12, the front end 13 is jet lower than the central part 8 and the front end 14 is set higher than the central part 8 and thus bending is made in steps so as to show up gradients from the left to the right. On the contrary, the rear end 15 is higher than the central part 8 and the rear end 16 is lower than the central part 8 and thus bending is made in steps so as to show down gradients from the left to the right.