We have been developing a novel capacitance type force sensor that enables simultaneous measurement of a torque around the vertical axis as well as normal and two orthogonal shear forces on the skin surface. In our previous research, the prototype sensors were made and authenticated the potency. Prototype sensors are parallel plate type collocated a dielectric between two circuits. We have planned to use an approximated displacement-capacitance characteristic curve when we estimate an output force. Therefore, this paper reports about an ideal approximation of the curve and several applications, such as surgical robot and nursing-care system.