For disposing projections of insulating film protruding into a hollow part in CMUT in order to suppress injection of electrical charge into the insulating film due to contact of a lower surface of a membrane with a lower surface of the hollow part, there are provided a structure of disposed projections preferred for suppressing increase in driving voltage for CMUT and decrease in receiving sensitivity, and an ultrasonic diagnostic apparatus using the same. The ultrasonic transducer of the present invention comprises a first electrode, a lower insulating film formed on the first electrode, an upper insulating film provided so as to form a hollow part above the lower insulating film, and a second electrode formed on the upper insulating film, and is characterized in that the lower insulating film or the upper insulating film has projections on the side of the hollow part, and the first electrode or the second electrode has openings formed at positions corresponding to the positions at which the projections are formed.
