An ultrasonic sensor for detecting an object includes: a piezoelectric element having a piezoelectric body and first and second electrodes for sandwiching the piezoelectric body; an acoustic matching element having a reception surface, which receives an ultrasonic wave reflected by the object; and a circuit electrically coupled with the piezoelectric element via a wire. The piezoelectric element is embedded in the acoustic matching element so that the acoustic matching element covers at least the first electrode, a part of a sidewall of the piezoelectric element and a part of the wire between the circuit and the piezoelectric element, and the sidewall of the piezoelectric element is adjacent to the first electrode.