In a DC-DC converting circuit, a charge pumping part receives an input voltage, a first clock and a second clock and outputs first and second voltages to first and second nodes, which are boosted by high voltages of the first and second clocks with respect to the input voltage. An output part is connected to the first and second nodes of the charge pumping part, and a level boosting part turns on or turns off the charge pumping part in response to the first and second clocks. The output part outputs the first and second voltages through an output terminal during a high period of the first clock and during a high period of the second clock, respectively. Thus, an output voltage having a voltage level corresponding to two times that of the input voltage may be output from the output terminal while the first and second clocks are provided.