In this paper, we propose a sensing system that can detect one dimensional tangential force on a forearm. There are some previous tactile sensors that can detect touch conditions when a user touches a human skin surface. Those sensors are usually attached on a fingernail, so therefore a user cannot touch the skin with two fingers or with their palm. In the field of cosmetics, for example, they want to measure contact forces when a customer puts their products onto their skin. In this case, it is preferable that the sensor can detect contact forces in many different contact ways. In this paper, we decided to restrict a target area to a forearm. Since the forearm has a cylindrical shape, its surface deformation propagates to neighboring areas around a wrist and an elbow. The deformation can be used to estimate tangential force on the forearm. Our system does not require any equipment for the active side (i.e. fingers or a palm). Thus a user can touch the forearm in arbitrary ways. We show basic numerical simulation and experimental results which indicate that the proposed system can detect tangential force on the forearm. Also we show some possible applications that use the forearm as a human-computer interface device.