A high voltage generator includes: a detection unit for comparing a reference voltage with a high voltage and detecting a voltage level of the high voltage; an oscillator selection unit for generating a first control signal and a second control signal in response to an output signal of the detection unit and a selection signal corresponding to a data operation mode; an oscillator for generating clock signals having different frequencies in response to the first control signal and the second control signal; and a pumping unit for generating the high voltage by performing a charge pumping operation in response to the clock signals.