A vehicle power supply device which prevents a lack of power supply to the motor and insufficient recovery of regenerative electric power of the motor at the time of switching between power running and regeneration. First input-output sections (3a, 3b) of a first DC-DC converter (3) are connected to second input-output sections (4d, 4e) of a PDU (4), second input-output sections (3c, 3d) of the first DC-DC converter (3) are connected to a fuel cell (1) and a capacitor (2), first input-output sections (20a, 20b) of a second DC-DC converter (20) are connected to second input-output sections (4d, 4e) of the PDU (4), and second input-output sections (20c, 20d) of the second DC-DC converter (20) are connected to a lithium-ion battery (21). A voltage control means (31) places the first DC-DC converter (3) or the second DC-DC converter (20) in a direct connection state and controls an output voltage of the other DC-DC converter according to an output voltage of the DC-DC converter placed in the direct connection state during the power running of the motor (5) and during regeneration thereof.