This invention provides a technique whereby, even if a step is produced by splitting a lower electrode into component elements, resistance increase of an upper electrode, damage to a membrane and decrease of dielectric strength between an upper electrode and the lower electrode, are reduced. In an ultrasonic transducer comprising plural lower electrodes, an insulation film covering the lower electrodes, plural hollow parts formed to overlap the lower electrodes on the insulation film, an insulation film filling the gaps among the hollow parts, an insulation film covering the hollow parts and insulation film, plural upper electrodes formed to overlap the hollow parts on the insulation film and plural interconnections joining them, the surfaces of the hollow parts and insulation film are flattened to the same height.