PURPOSE: To simplify a structure by a method wherein a movement of the door in a safety device of a high frequency device is transmitted to the door key, reeived at once by the first lever and a switch is operated by the second lever.

CONSTITUTION: When the door 21 is to be closed, the door key 24 is pushed in and the first lever 26 is moved. At this time, the second lever 27 is abutted against the stopper 30 and is not moved, the switch 29 is kept open. When the heating start-up button 31 is depressed, the stopper 30 is moved, the abutment against the second lever 27 is released, the second lever 27 and the fitting 32 are moved under a pressure of the spring A 28 to push the switch 29, thereby kept closed, and a heating is started. When the door 21 is opened under this condition, the door key 24, the first lever 25 and the second lever 27 returned to their original position by a returning force of the switch 29 and a repletion of the spring B 34, the switch 29 is opened, the heating is terminated, the stopper 30 is also returned by a tension force of the spring C 35.