A back-bias voltage generating circuit controls the back-bias voltage in a predetermined range by detecting the back-bias voltage in case the back-bias voltage level decreases below a predetermined target level. The circuit includes first and second detecting units outputting respective detection signals, which detect a voltage level of the terminal based on respective higher first and lower second target levels. An oscillator generates an oscillation signal that oscillates at a predetermined frequency, in response to a detection signal of the first voltage detecting unit. A charge pumping unit drives the terminal by performing charge pumping in response to the oscillation signal. A voltage level control unit controls the voltage level of the terminal in response to the detection signals, whereby the terminal's voltage level is lower than the first target level and higher than the second target level.