An apparatus for generating an internal voltage includes an output-voltage detecting unit for detecting a voltage level of an internal voltage, an oscillating unit for generating a periodic signal in response to a detection signal from the output-voltage level detecting unit, a first driving-voltage level detecting unit for detecting an increase of a voltage level of a driving voltage, a second driving-voltage level detecting unit for detecting a decrease of a voltage level of the driving voltage, a period control unit for controlling a period of the periodic signal in response to output signals of the first and second driving-voltage level detecting units, and a charge pumping unit for generating the internal voltage by charge-pumping the driving voltage in response to an output signal from the period control unit.