According to the present invention, a power supply control device for an electric power steering device used for a power supply system comprises a main battery 40 connected to the electric power steering device via a first power supply line and a sub-battery 50 connected to the electric power steering device via a second power supply line, wherein when detecting the state of the sub-battery, said power supply control device restricts or disconnects power supply from the main battery to the electric power steering device while it permits power supply from the sub-battery to the electric power steering device, characterized in that said power supply control device prevents the detection of the state of the second battery if a vehicle speed is higher than a predetermined reference value.