The importance of wearable devices in nursing care and rehabilitation has been strongly recognized. The purpose of our study is to develop a flexible displacement and bending sensor which can measure human movement and the movement of a flexible actuator. In this paper, a skin displacement sensing system using a flexible string-like flexible displacement sensor to measure the body movement, i.e., measuring the displacement of the skin, was proposed and tested. A flexible linear encoder that can measure the displacement of the flexible pneumatic cylinder using four photoreflectors was also developed. In addition, the measurement using both sensors was done to measure the human motion and the flexible actuator.