An ultrasonic transducer includes a case, a reflective portion, and a piezoelectric body. The case has a substantially cylindrical shape including one closed end in the center axis direction that defines a top. The piezoelectric body is disposed on the inner surface of the top of the case. The reflective portion is arranged to oppose and be spaced apart from the piezoelectric body. The distance between the piezoelectric body and the reflective portion is greater than the maximum displacement of the piezoelectric body and is substantially an odd number multiple of a ¼ wavelength of sound waves or less than or equal to the ¼ wavelength.