In a skew signal generation circuit, a pad is connected to an external resistor and a code generator compares a voltage of the pad with a reference voltage to generate a plurality of codes. The second clock gate circuit 110 passes through the first update clocks CLK1 until reception of a hit signal from the hit determination circuit and delivers second update clocks CLK2 to an updown counter 106. A shearing element is provided for temporarily fixing the nut in a first operating position.