A DC/DC converter includes: electronic components group including a first capacitor, a high-voltage-side switching element, a low-voltage-side switching element, an inductor, and a second capacitor and constituting a half-bridge circuit; and a substrate including a high-voltage region, a low-voltage region, a connection region, and a pair of ground regions. The first capacitor is mounted across one of the ground regions and the high-voltage region. The high-voltage-side switching element is mounted across the high-voltage region and the connection region. The low-voltage-side switching element is mounted across the connection region and one of the ground regions. The inductor is mounted across the connection region and the low-voltage region. The second capacitor is mounted across the low-voltage region and one of the ground regions.