Railway accidents during operation, such as derailment or collision of trains, can cause many casualties. To prevent such train accidents, automatic train stop (ATS) devices are used as the most basic safety devices on all railway lines. The ATS-S1, used on some Korea Railroad’s conventional railway lines, only sounds an alarm at the stop signal and is released by confirmation of the driver's handling. In this case, risk factors exist for accidents such as entry of danger zone and speeding due to human error. Therefore, we propose a method to improve the ATS system which can prevent over speed by continuous surveillance of the train speed and thus prevent train accidents due to human error by the driver.