IN-VEHICLE POWER SUPPLY DEVICE

An in-vehicle power supply device includes a voltage conversion unit and a control unit. The control unit performs first control to cause the voltage conversion unit to perform only a step-down operation, second control to cause the voltage conversion unit to perform only a step-up operation, and third control to cause the voltage conversion unit to perform both the step-down operation and the step-up operation. The control unit performs the third control if a first duty of an on-off signal provided to a first switching element becomes an upper limit threshold or greater in the first control or if a second duty of an on-off signal provided to a second switching element becomes a lower limit threshold or less in the second control.