PURPOSE: To increase durability and also give ER effect even at low voltage by positioning electrodes opposed to each other on both sides of an electroviscous fluid, coating the electrodes with insulating layer, and applying AC current to both electrodes.

CONSTITUTION: A device is composed of an electroviscous fluid, electrodes opposed to each other electrically on both sides of the electroviscous fluid, and a power unit for applying AC voltage to the electrodes and, at least either one of the electrodes is coated with insulating layer. For the insulating layer, oxides such as, for example, zirconium oxide, etc., inorganic carbide such as silicone carbide, etc., or heat-resistant organic matter is used to insulate the electroviscous fluid from the electrodes. When AC voltage is applied to the electrodes, the lowering of ER effect (electroviscous effect) due to voltage drop can be suppressed as compared with DC voltage. Thus the device can be driven at relatively lower voltage than DC electric field and, in addition, it is superior in durability.