The present invention realizes a DC-DC converter that is provided with a reverse flow protection function, while reducing conduction loss. A DC-DC converter includes: a voltage conversion unit that steps down a voltage applied to a first conductive path and output the resulting voltage to a second conductive path; a reverse flow state detection unit that detects a reverse flow state of a current flowing through the second conductive path; and a reverse protection control unit that performs a protecting operation when a current flows in a reverse direction. A switching element is provided on a third conductive path that is located between a voltage conversion unit and a reference conductive path, and the reverse protection control unit operates to switch the switching element to an OFF state upon a reverse flow state being detected.