An innovative sensor is developed to evaluate hardness of human soft tissue. This sensor provides easy and accurate hardness measurements based on a unique sensing mechanism. Hardness of soft materials is often evaluated by using international standards of hardness such as IRHD (International Rubber Hardness Degree) and durometer hardness. However the conventional scales based on these standards requires a stable pressuring condition to the target. Therefore, these scales cannot be used for targets that are in motion or targets that require quick measurement such as human muscles during exercises and a liver exposed at a surgery. The prototyped sensor has a compact body and allows continuous hardness measurement with an arbitrary pressing force. This sensor always monitors the force exerted on the sensor and automatically eliminates the unintended effect from the fluctuation of the pressing force. Therefore, continuous time series of the hardness data is real-timely available. This paper reports results of a test as well as the detail of the mechanism and data processing technique of the latest version of the sensor.