PURPOSE: To increase the range of a use for a driving source, by joining an ion stretchable material to a stationary end and moving end.

CONSTITUTION: Liquid having given ion concentration is fed through a piping 19 to the opposite side to the side which is desired to be moved, and the liquid is circulated through a piping 17. Simultaneously, the liquid is fed through a piping 20 to the side where pure water is driven, and it is circulated through a piping 15. This enables to perform driving of the right side. Conversely, when driving of the left side takes place, the pipings 19, 17, 20, and 15 are closed, pipings 18 and 16 are opened, the liquid is circulated within the left side with the aid of a pump P1 on a pure water route, pipings 21 and 14 are opened, and the liquid circulated within the right side with the aid of a pump P2.