A DC/DC converter (100) is configured by connecting a first switching circuit (5) between a DC power source (1) and a first winding (3a) of a transformer (3), and connecting a second switching circuit (8) between a battery (2) and a second winding (3b). When charging the battery, a control circuit (20) controls the phase shift amount (theta 1) of a first diagonal element, and the phase shift amount (theta 2) of a second diagonal element inside a second switching circuit (8), relative to the drive phase of a first reference element inside a first switching circuit (5). When the charging current during a boost charging control period is positive or 0, the control is performed in a manner such that the phase shift amount (theta 2) exceeds the short-circuit prevention time for each semiconductor switching element and is larger relative to the phase shift amount (theta 1). As a result, it is possible to resolve boost inoperability caused by short-circuit prevention time, and to improve the controllability of a boost control.