A vehicle-surroundings monitor apparatus according is provided with a sensor having a transmission/reception means for transmitting an ultrasonic wave to surroundings of a vehicle and receiving a reflected ultrasonic wave from the surroundings, a transmission circuit for generating an ultrasonic wave to be transmitted from the transmission/reception means, and a reception-processing means for processing an ultrasonic wave received by the transmission/reception means, and a control means for supplying a power-supply voltage to the sensor. A power-supply voltage supplied by the control means to the sensor is split into a power-supply voltage to be supplied to the transmission circuit and a power-supply voltage to be supplied to the reception-processing means.