An atomic clock utilizing the Stark effect has been designed and constructed. In this clock, the error caused by the reflections in the microwave circuits has been successfully reduced to within the error by random noises, and the authors are sure of its possibility of long time operation. The accuracy has been estimated to be about 5×10−9from observation of the received frequency of the standard station JJY, and comparison with the frequency of a quartz chronometer. The various components of this clock are described in detail, and the theoretical limits of the accuracy are also discussed.