A step-up power supply unit for providing a multiplicity of different step-up voltages as needed, generated by stepping up a voltage of a single power source such as a battery. The step-up voltage of the last stage charge pump unit and the step-up voltage of at least one charge pump unit other than the last stage charge pump unit, are made available as multiple output voltages. When one or more of the output voltages are not needed, all the charge pump units subsequent to the one providing the highest output voltage are disabled based on an output voltage control signal, thereby minimizing the size and cost of the step-up circuit and reducing the power consumption by the circuit.