To make a shunt resistor unneeded and to respond at high speed to an abnormal current in the case of an imperfect layer short-circuit, by constituting a full-bridge a DC-DC converter with the second main electrodes of first and second semiconductor elements, the first main electrode of third and fourth semiconductor elements and a load having first and second terminals.

An n-channel first switch circuit 801 has a first main electrode terminal DA1 connected to an external input terminal T1, a second main electrode terminal SA1 connected to a first external output terminal T3, and a control electrode terminal GA1. Another n-channel second switch circuit 802 has a first main electrode terminal DA2 connected to the external input terminal T1, a second main electrode terminal SA2 connected to a second external output terminal T33, and a control electrode terminal GA2. This control circuit detects an abnormal current in either one of the first switch circuit 801 and second switch circuit 802. If an abnormal current occurs, one of the first and second switch circuits 801, 802 is controlled in such a way as to be turned on or off in order to generate current oscillation, which breaks the first and/or second switch circuits 801, 802.