An ultrasonic sensor includes a cylindrical casing having a bottom portion. The casing has a piezoelectric element on a bottom surface thereof. A substrate is attached to an end surface of an opening portion of the casing with a damping member provided therebetween such that the damping member covers the opening portion. Pin terminals are arranged so as to extend through the substrate and the damping member and are electrically connected to the piezoelectric element with lead wires. An inner space of the casing is filled with foamable resin.