The ultrasonic sensor includes: a plurality of transmission/reception dual-use elements, first electrode switches connected to the first electrodes of the transmission/reception dual-use elements; second electrode switches connected to the second electrodes of the transmission/reception dual-use elements; a control circuit; a transmitting circuit; a receiving circuit; a common-electrode connection wiring; and serial connection wiring. When an ultrasonic signal is to be transmitted, the control circuit connects the first electrode switches to the transmitting circuit, connects the second electrode switches to the common-electrode connection wiring so that the transmission/reception dual-use elements are connected in parallel to the transmitting circuit and the common electrode. When an ultrasonic signal is to be received, the control circuit connects the first electrode switches and the second electrode switches to the serial connection wiring so that the transmission/reception dual-use elements are serially connected to the receiving circuit.