Abstract: There is provided an ultrasonic sensor including: a closed-bottom tubular case including a bottom portion and a tubular portion; and a piezoelectric element joined to an inner bottom surface of the closed-bottom tubular case. A porous elastic body is in close contact with the inner bottom surface to include a portion at which an amplitude is maximum in the inner bottom surface when transmitting or receiving an ultrasonic wave in the inner bottom surface. An elastic body having a density higher than a density of the porous elastic body is in close contact to an opening side of the closed-bottom tubular case to include a portion at which vibration is transmitted from the inner bottom surface to the tubular portion of the closed-bottom tubular case.