This invention includes a first electrode which is fixed on a base, a vibration film which is disposed to oppose the first electrode with an air and vacuum portion between the vibration film and the first electrode, a second electrode which is supported by the vibration film and is connected to a predetermined potential, a ferroelectric which is electrically connected to the first electrode, and a driving portion that applies, to the first electrode, a driving signal which is a monopulse voltage signal and whose polarity is reversed every time the driving signal is outputted.