To improve the performance of a sensor element.

The sensor has at least one hollow part inside an elastic body, and gas and/or liquid or jelly liquid is enclosed in the hollow part. The gas and/or liquid is enclosed under the use environment with the pressure value inside the hollow part in the range from below the external pressure almost to the equal value if the external stress applied from an object of measurement is from zero to the minimum value, or with the pressure value inside the hollow part in the range larger than the external pressure if the external stress applied from the object of measurement is the maximum. Accordingly, the internal pressure enclosed in the elastic hollow body can be minutely adjusted. In addition, when the sensor is used as a cardiac pulse sensor of a human body, the human body structure is considered as the elastic hollow body sealed with a pressure value, so that the characteristics and structure similar to those of the human body structure can be obtained. Further, signals are not attenuated inside the hollow part like in the human body structure, so that an ideal transmission passage without orientation and without receiving noise can be formed. Since the performance of the sensor is not affected by incorporating electric parts etc., in the hollow part, a micro-measuring instrument can be incorporated in the sensor.