To enable speedy compliance by providing an electric viscous fluid, of which the viscosity is changed corresponding to a feedback signal from the main body of a machine to input, at the position to become the resistance of inputting.

A metal contact 3 and an electric viscous fluid 4 (sealed in a flexible container) are held between upper and lower holders 2. The electric viscous fluid 4 is provided with an electrode 5 to load a voltage for changing viscosity, and wiring 6 for input is connected to the metal contact 3 as well. Since the viscosity of this fluid is low while no electric charge is loaded to the electric viscous fluid 4, almost there is no resistance at the time of pressing. There is only the resistance of a spring for holding and there is no difference from an ordinary switch. When the viscosity of the electric viscous fluid is increased, however, it becomes resistance at the time of pressing, and much more power is required for connecting both the contacts. Then, the feedback signal from the machine is inputted to the electrode 5 in order to increase the viscosity of the electric viscous fluid.