This invention prevents defects generated when a bonded substrate stack having a separation layer is separated. The ladder resistor includes a plurality of resistors series-connected to each other and is supplied with a correction voltage at least one of both ends of the series connection and a plurality of connection points in the series connection to generate a plurality of gradation voltages at the plurality of connection points. The locking member has one or more fingers to engage the nut with an end of the finger being displaced to engage the nut as a result of deformation of a finger actuating tab or a dished body of the locking member. A plurality of blade assemblies are disposed on the rotor having blades extending radially outwardly from the axis of the rotor wherein at least at times one or more of the blade assemblies are disposed between one or more of the tines.