To improve the adjustment accuracy by suppressing an on resistance of a semiconductor switch low in the adjustment process or the like by providing a voltage terminal to which an external high voltage is applied in addition to an inner power supply terminal to the circuit.

In the adjustment process, a low voltage internal power supply is applied to a 1st power terminal 18 and an external high voltage power supply is applied to a 2nd power terminal 19. Then the low voltage internal power supply is supplied to a regulator 12 to drive an IC section 5 and the external high voltage power supply is fed to a semiconductor switch 27 of a changeover circuit 10. Even when the semiconductor switch 27 of the changeover circuit 10 is frequently switched, the ON-resistance is suppressed, resulting that the adjustment accuracy is considerably improved. Furthermore, the external high voltage power supply from the 2nd power supply terminal 19 is not supplied to the regulator 12 by means of a diode 23 and then a voltage higher than the specified voltage is not applied to other circuits.