This study was performed to develop a non-destructive inspection system to detect grinding burn, which is capable of quantitative 100% inspection inside a production line. An eddy current sensor, which has advantages of short inspection time and low cost, was used. It was shown that the grinding burn detection technique had been developed and is possible to detect grinding burn by using this technique, in the 1st report 1)and the 2nd report2). In this report, an experiment of in-process detection of grinding burn was conducted, by applying the grinding burn detection technique which we have developed. The eddy current sensor has been combined with an in-process gauge in order to keep the clearance between the sensor probe and the work piece constant. It was shown that grinding burn can be detected successfully during cylindrical machining.