To provide a vehicular power supply device capable of rapidly stopping the power supply from a battery to an electric load when some trouble occurs in a vehicle.

A battery (112) is stored in a first casing (110), and a control unit (122) and a cutoff means (124) are integrated with each other as an electric circuit unit (120). The electric circuit unit is stored in a second casing, and the first and second casings are assembled to each other. A connection terminal for supplying the power to an electric load from the battery via the cutoff means is provided outside the second casing. The control unit drives the cutoff means to cut off the power supply to the electric load from the battery when receiving the collision detection signal, the fuel leakage detection signal, the drive prohibition signal of the electric load, or the like.