the status of an actual warning sound during automatic closing of the opening and closing door as shown in fig6 a and 6b the sound settings for the warning sound can be set according to whether the current opening and closing door operation is a door opening operation or a door closing operation and also according to the current open distance l in each operation in other words as shown in fig6 a during automatic opening the pitch can be raised as the open distance l is increased by opening the door as the maximum open distance lmax is greater the maximum value of the pitch can also be raised meanwhile as shown in fig6 b during automatic closing the pitch can be raised as the open distance l becomes shorter by closing the door in this instance also as the maximum open distance lmax is greater and the open distance becomes closer to the complete closing the pitch can be raised furthermore these sound settings can be made according to the opening closing speed of the opening and closing door the maximum open distance and the user 39 s use conditions or the properties of the heated object for example it is preferable to set a sound with higher warning ability as the.