circuit 50 and the phase compensation resistor 60 are identical with those in the first embodiment a difference from the first embodiment resides in that the switch 70 and the undershoot and overshoot improving circuit 100 are removed from the voltage regulator and the switch 80 and the overshoot improving circuit 90 are inserted into the voltage regulator the overshoot improving circuit 90 includes pmoss 1 to 3 nmoss 5 and 6 constant current circuits 8 and 9 and an lpf 11 the switch 80 includes an nmos 7 the overshoot improving circuit 90 is connected to the output terminal of the voltage regulator and detects an ac component of the output voltage when the output voltage fluctuates to thereby control the switch 80 to short circuit the voltage divider resistor 50 in the overshoot improving circuit 90 the pmoss 1 and 2 the nmoss 5 and 6 the constant current circuit 8 and the lpf 11 are identical with those in the undershoot and overshoot improving circuit 100 a difference from the first embodiment resides in that the pmos 4 and the constant current circuit 10 are eliminated further the drain electrode of the pmos 3 is connected to the switch 80 the nmos 7 has a gate electrode connected to an output terminal of the overshoot improving circuit 90 a source electrode connected to the ground terminal and a drain electrode connected to the output terminal of the voltage regulator when undershoot occurs signals are input to the differential pair in the same manner.