PURPOSE: To set a ratio between a threshold voltage and a power supply voltage for an inverter circuit without being affected by process dispersion, temperature fluctuation or power supply voltage fluctuation by supplying a voltage proportional to the power supply voltage to the inverted input terminal of an operational amplifier by two resistors.

CONSTITUTION: Since resistors 3 and 4 serially connected between a first power source VDD and a second power source 11 is monolithically constituted, the matching ability of characteristic is made satisfactory and the potential and power supply voltage can be set at the fixed ratio. Therefore, the potential of a contact B being the threshold voltage of an inverter circuit 12 can be set at a certain ratio of the power supply voltage as well. The inverter circuit 13 matches the characteristic with the inverter 12. Then, the ratio between the threshold voltage of the inverter circuit 13 and the power supply voltage can be set constant. Thus, the ratio between the threshold voltage and the power supply voltage for the inveter circuit can be set without being affected by the process dispersion, temperature fluctuation and power supply voltage fluctuation.