PURPOSE: To obtain the reference voltage of high accuracy without increasing an occupying area of a FET by utilizing the difference of threshold voltage between two N channel MOSFETs as the reference voltage.

CONSTITUTION: A completely the same process as a boron injection process dropping the threshold voltag of P channel MOSFETs 21, 23 filling the role of a constant-current source at the positive power supply VDD side grounded is executed to the first N channel MOSFET 22, the threshold voltage of the FET 22 is increased, and the difference of the threshold voltage with the second N channel FET24 is outputted as output voltage V3. A fixed value which does not depend upon supply voltage is obtained as the voltage V3 because a gate of the P channel FET23 is wired to a gate of the FET21 at that time.