A mobile object includes a wall member to which an ultrasonic sensor is fixed. The wall member has a through hole through which an oscillating face of the ultrasonic sensor is exposed from the wall member. A closing member closes a gap generated between the wall member and the ultrasonic sensor. The closing member connects an edge of the through hole located outside of the wall member and an edge of the oscillating face of the ultrasonic sensor. The closing member has an outer face exposed from the wall member, and the outer face of the closing member has asperities.