PURPOSE: To improve safety by a method wherein a locking device is connected to a cam to prohibit the action of the cam when the temperature inside an oven exceeds a specified temperature, and the connection between the locking device and the cam is released when the temperature inside the oven drop below the specified temperature.

CONSTITUTION: When the temperature inside an oven exceeds a specified temperature, 300°C for example, because of self-cleaning operation, a locking device 30 is turned with a rise in temperature and connected to a cam 30, so that the cam 30 is prohibit from acting and an oven door is automatically kept in closed state. When self cleaning operation is completed and the temperature inside the oven drops below the specified temperature (about 300°C), the locking device 30 is reversed in response to the fall of temperature, so that the connection between the locking device 30 and the cam 20 is released and the oven door is returned to openable state. Thus, the locking device excellent in safety can be obtained.