To apply higher voltage by restricting generation of dielectric breakdown when applying high voltage, and as a result, to realize larger electrorheological effect to improve performance of a device and miniaturize the device, the device using ER fluid (including ER gel).

This method of controlling viscosity of ER fluid by applying voltage to the ER fluid is structured of a voltage applying method for applying voltage, allotting to a positive and a negative codes and a method of arranging electrodes in order of a positive electrode substrate/ER fluid/an output substrate/ER fluid/a negative electrode substrate. As a result, ER effect of the device using ER fluid is remarkably improved, and practically, performance of the device is improved and the device can be miniaturized. Alternately, reduction of potential on an output side in application of high voltage to zero is enabled, and electric shock and static dielectric breakdown on an output side can be restricted. This method can be used in a wide range of various device using ER fluid such as a clutch, a brake, a damper, a tension controller, a grip, a valve and inner force sense presentation.