An apparatus for performing a function by using a fluid, which includes: a mass of a fluid whose viscosity varies with an electric current applied thereto; a pair of electrodes which are disposed so as to apply the electric current to the mass of the fluid; a device for controlling a voltage to be applied between the pair of electrodes to substantially change the viscosity of the mass of the fluid; and electrically resistive layers each having a predetermined electrical resistance value and covering each of the pair of electrodes, each of the resistive layers consisting of an insulating material having a low electrical conductivity. Thus, the present apparatus is capable of restricting an increase in an electrical current consumed by the mass of the fluid, when an electrical resistance value of the mass of the fluid is lowered due to a rise in an operating temperature of the mass of the fluid.