A power supply circuit is provided which is capable of preventing a drop in an output voltage of the power supply circuit used as a DC/DC converter made up of single and conductive type (n-type or p-type) MOS transistors and of improving efficiency. Since a control voltage having an amplitude [2×VDD] is applied from a level shift circuit to a charge-pump circuit, even when potentials at nodes becomes a level [2×VDD], pMOS transistors are kept in an OFF state, thereby preventing leakage of currents from pMOS transistors. This avoids a drop in an DC output voltage. As inputs to the level shift circuits, potentials at nodes of the charge-pump circuit are used and, therefore, even if potentials at nodes of the level shift circuits are high, pMOS transistors are kept in an OFF state.