The temperature increase due to urbanization, i.e. urban heat island, is becoming very serious in Japanese cities in summer. In this study, the urban thermal environment in Tokyo metropolitan area is analyzed and forecasted by means of a meteorological meso-scale model based on the Mellor-Yamada model level 2.5 incorporating an urban canopy model. Increase of total floor space in 2020 based on projected population is estimated firstly. Furthermore, the progress of the heat island is analyzed with several scenarios of various urban forms in 2020.