To fix a ferroelectric core to an electric conductor support, without causing a play or twist by providing a slit ring spring between the core and support.

A ring spring 10 has a slit 11 and is made of a nonferroelectric metal material. The slit is to electrically cut off the spring itself. The spring has outer slit teeth 12 twisted around radial axes to realize a spring action. The ring spring with slit has inner slit teeth and gear-like teeth and is disposed between a ferroelectric core and electrode conductor support.