A reception unit receives, with an ultrasonic sensor, received signals including a reflected wave obtained when an acoustic signal emitted from a mobile body is reflected by an object. A disturbance judgment unit judges whether a jamming attack in which a jamming signal is transmitted from outside is being made, on the basis of the received signals. An object detection unit detects an object in surroundings of the mobile body on the basis of the received signals if it is judged that no attack is being made and does not perform object detection if it is judged that an attack is being made.