the sensor or the photo coupler connected to the lamp whether the state of the mechanical manipulation unit 100 has been switched subsequently the controller 130 determines whether child lock has been set that is upon determining that there is no child lock after the state of the mechanical manipulation unit 100 has been switched the controller 130 switches the dc relay 120 to an on state on the other hand upon determining that there is child lock the controller 130 maintains the dc relay 120 in an off state fig6 shows a state in which the electric heater 110 is driven as a result of the mechanical manipulation unit 100 being operated in a state in which child lock has not been set at this time the user may manipulate the child lock input unit 140 see fig3 that is the user may input or release child lock through the child lock input unit 140 since the controller 130 has already known a state in which the electric heater 110 is driven the controller 130 may disable the child lock input unit 140 in a state in which the heater 110 is driven that is the controller 130 may control child lock not to be set in a state in which the heater 110 is driven since the heater 110 is driven on the premise that child lock has been set release of child lock does not occur in a state in which the heater 110 is driven conventionally when child lock is set in a state in which the electric heater 110 is driven the controller may turn the nc type ac relay off as a result driving of the electric heater is stopped even though the mechanical manipulation unit is operated that is driving.