A reference voltage generating circuit includes voltage outputting means for outputting a reference voltage corresponding to a difference between a band gap reference voltage and an input voltage; a first resistor having one end that is coupled to the output of the voltage outputting unit; first variable resistor unit having a plurality of second resistors that are serially coupled between the first resistor and a ground voltage, for providing the input voltage of the voltage outputting unit with a first trimming voltage that is inputted to one end of selected one of the plurality of the second resistors in response to decoded signals for trimming the reference voltage; second variable resistor having a plurality of third resistors coupled serially between the first resistor and the ground voltage, the third resistors having different resistances from the second resistors, for providing the input voltage of the voltage outputting unit with a second trimming voltage that is inputted to one end of selected one of the plurality of the third resistors in response to the decoded signals for trimming the reference voltage; and selecting unit for selectively providing the first trimming voltage or the second trimming voltage to the input voltage of the voltage outputting unit.