In these 10 years, the number of patients hospitalized by heat disorders has been continuously increasing. Especially in urban cities heat islands effect makes the environment worse, and it affects increase of patients especially in elderly people. In 2007, at Tokyo metropolitan city (population is around 12 million), 1,268 people had been taken to hospitals by ambulance cars, and aged patients older than 65 years old exceeded to 40 percents. The Ministry of Environment publishes ‘A guideline for preventing heat diseases' from 2005 annually, and National Institute for Environmental Studies and Japan Meteorological Business Support Center have been managing a web site regarding heat disorders to reduce and to warn its risks to the public. As an index for warning heat disorders, WBGT (Wet Bulb Globe Temperature) is widely used in Japan, because the index has been used in exercise physiology and in labor hygiene studies from 90s. The web site for warning heat diseases is consist of (1) 2 days forecasts calculated from JMA-NWP, (2) actual WBGT situation with observed at meteorological observatories and (3) prompt report of heat diseases patients with reports from local emergency services.