A power voltage of a battery (including a secondary battery) mounted on a portable device drops with use or the like of the portable device. Therefore, a step-up switching voltage regulator circuit is mounted on the portable device. On the other hand, the power voltage of the battery exceeds a voltage necessary for driving the portable device sometimes when the battery is fully charged. In this case, when the step-up switching voltage regulator circuit is driven, the power is consumed in vain, and a burden is imposed on the battery. The step-up switching voltage regulator circuit of the present embodiment switches an output in accordance with the power voltage, that is, raises the power voltage supplied from the battery to a predetermined output voltage, and outputs the output voltage, when the power voltage supplied from the battery is smaller than the predetermined output voltage; on the other hand, the step-up switching voltage regulator circuit outputs the power voltage supplied from the battery as the output voltage, when the power voltage supplied from the battery is larger than the predetermined output voltage; and consequently, in the step-up switching voltage regulator circuit, the burden on the battery mounted on the portable device can be reduced.