PURPOSE: To prevent energizing to a heater circuit in the case a mobile board is opened, to prevent a burn in equipment or clothes or the like and to enhance safety by fixing a switch device for opening/closing the heater circuit linked with the opening/closing the mobile board which is connected to a fixing board to be freely rotatable.

CONSTITUTION: The mobile board 10 is connected to the fixing board 8 having a heater so as to be freely rotatable and a switch device 15 for opening/closing a heater circuit linked with the opening/closing of the mobile board 10 is fixed. That is, the heater circuit is not energized in spite of the depression of a switch button 21 which is directly connected to the heater circuit in the case, the mobile board 10 is opened so that the burn in the equipment and the clothes or the like is prevented and also safety is enhanced.