Early warning systems using real-time earthquake information, based on the nation wide earthquake observation networks in Japan, can be applied for earthquake damage mitigation in various fields. The ideas of the early warning system are to give an alarm before strong shaking occurs, to countdown for the S-waves arrival to the site and to predict the expected seismic intensity of ground motion. The authors have developed an application of real-time earthquake information for disaster prevention in schools. This application was installed at Nagamachi Elementary School in Sendai, a one million population city in Japan, which has a high probability of being shaken by the Miyagi-Ken Oki earthquake with an epicentral distance of about 120 kilometers. This paper describes the early warning system. The hardware comprises a receiver of real-time earthquake information via satellite, a PC server, a LAN system for voice/image transmission and a broadcasting system for voice information. The software comprises three functions; 1) Evacuation mode (Early warning for JMA intensity more than IV), 2) Training mode (Early warning for JMA intensity less than III or manual setting, 3) Education mode (Static Screen" and "Dynamic Screen" which shows pictures of earthquake damage and the animation of human and structural behavior during earthquakes respectively). An early warning can be announced via speakers to all the school and via voice/image in the teacher's room and the model class about 15 seconds before the S-wave arrives at the elementary school. About 800 pupils have performed an evacuation drill using the system. Questionnaire investigation after the drill has been performed to confirm the effectiveness of the system.