Disclosed is an improved construction of an ultrasonic transducer, wherein a charge is not easily injected into an insulating film even when the bottom of a membrane comes in contact with a lower electrode, and a manufacturing method thereof without using the wafer laminating technique. The ultrasonic transducer includes a lower electrode; a cavity layer formed on the first electrode; an insulating film covering the cavity layer; and an upper electrode formed on the insulating film, wherein, the cavity layer includes projections formed into an insulating film protruded from the cavity layer. In addition, an opening is formed into the upper electrode, and this upper electrode having the opening formed therein is deposited at a position not being superposed with the projections of the insulating film when seen from the top.