To improve the safety of railways in snowy regions, we are developing a new alarm system for preventing avalanche disasters. This system is composed of a detecting unit, signal conversion device and alarm device. The detecting unit installed at a slope subject to avalanches detects vibration due to avalanches strike with a built in small vibration sensor. Operating tests of the new system were carried out using a snow avalanche chute at the Shiozawa Snow Testing Station. The tests revealed that the system can not only detect the occurrence of avalanche, but also judge its scale. Trains may securely be stopped by this system, therefore, when an avalanche has occurred.