Abstract: A power supply system for a vehicle is provided which is able to supply an electric brake apparatus with necessary power even if an abnormal condition occurs in a battery or a conductor which is connected to the electric brake apparatus. A relay control unit 12 normally brings a relay 11 in a state in which its input terminal is connected to an A terminal 13. This causes a generator 50 or main battery 20 to supply an electric brake apparatus 100 with power via first and second power supply lines 40 and 41 and charges an auxiliary battery 21. If an abnormal condition occurs at main and auxiliary batteries 20 and 21, main and auxiliary power supply lines 30 and 31, first and second power supply lines 40 and 41, the relay control unit 12 brings the relay 21 into a state in which its input terminal is connected to A or B terminal 13 or 14 in response to the abnormal condition.