An extremal voltage detector produces an output voltage from an operational amplifier having its non-inverting input terminal connected to a first node and its inverting input terminal connected to a second node. A cathode of the photodiode is connected to a source of the reset transistor, and an anode of the photodiode is connected to ground. Other embodiments are also described. The divider circuit divides a voltage that appears on the internal node and provides a divided voltage. Each of the vibrating units is mounted on the inflatable body, and includes a vibrating plate that is spaced apart from the inflatable body and that is formed with protrusions thereon, and a driving member for driving vibration of the vibrating plate.