Provided is an integrated circuit package which complementarily switches on/off a MOS transistor Q1 (first switch) and MOS transistor Q2 (second switch) in accordance with an output voltage Vout, and which externally outputs a pulse signal having a fixed on-duty D during a step-up/step-down mode. The integrated circuit package has a determination unit 61 for determining the impedance of an external component connected to an external pin P5 that outputs the pulse signal to the exterior during the step-up/step-down mode, and determining whether the external component is a third switch on the basis of the impedance determination result.