VEHICLE POWER SUPPLY DEVICE

In order to detect failure of a charge/discharge current sensor for a battery and estimate and manage the state of charge of the battery when the charge/discharge current sensor has failed, provided are: a state-of-charge estimation unit for estimating the state of charge of the battery; an operation current estimation unit for estimating operation current of an electric load connected to the battery; and a charge/discharge current sensor failure detection unit for determining that failure occurs on the charge/discharge current sensor for detecting charge/discharge current of the battery, when a difference between the charge/discharge current and the operation current estimation value is equal to or greater than a predetermined value, wherein, when failure of the charge/discharge current sensor is detected, the electric load is operated at low output, and the state of charge of the battery is estimated using the operation current estimation value.