To enable a radio sensor device to carry out a conversion process from a detected value into a measured value, more effectively and more precisely.

The radio sensor device is equipped with: at least one sensor 101; a signal processing section 190 which converts the detected value S1 of the sensor 101 into the measured value S3 by applying it to approximate expression; and a transmitting circuit section 141 for transmitting the measured value S3 on the radio. The signal processing section 190 carries out the conversion by using different approximate expressions in accordance with the detected value S1. For example, a first least squares approximation polynomial is used for the conversion in the case the detected value S1 is in a first range, and a second least square approximation polynomial is used for the conversion in the case the detected value S1 is in a second range. Since the different approximate expressions are used for the conversion in accordance with the detected value S1 of the sensor 101 in order to derive the measured value S3, the used approximate expressions are made simple, and as a result, an arithmetic processing load can be reduced significantly.