It is well known that the existence of the city temperature was confirmed in various cities in Japan from the results of previous researches. However, temperature distribution is affected by many factors such as topographical situation, size and functional character of a city, and so on. So, selection of the city where these factors are as simple as possible becomes necessary for analysis of the detailed distribution of temperature in and around the city. Recently a special project for the investigation of city climate was undertaken by the Research Group of City Climate in Japan and an intensive observation was carried out in several cities from this point of view. The purpose of this paper is to analyze, by using the data from the above-mentioned project, the detailed distribution of temperature in and around any urban area located in the central part of a plain, which is thought to be not affected by surrounding topographical releafs without much influence of season and weather conditions. Kumagaya City is located near the center of the Kantô Plain and had a population of about 50, 000 in the urban area in 1956. There were neither houses and buildings constructed with concrete or stone, nor factories generating a large amount of heat. The urban area of Kumagaya City is represented by the lines of 10 percent building coverage as illustrated in Fig. 2. This area is shown with a darker tone in Figs. 2, 3, 4, 5. Observations were repeated in the ealy morning, daytime and night in each of four seasons from Septmber in 1956 to March in 1957. Intensive net-work of temperature obtained by mobile observation is represented on Fig. 1, using 2 sets of sensible thermistor thermometer mounted on the automobiles, Accuracy of the readings of thermometer is 0.2°C, and the representativeness of observed temperature is about 100m in the vicinity of the observation point in this study. Then, the results of observation are sufficiently able to clarify the purpose of this paper after time correction. Typical examples of the temperature distribution in Kumagaya City are shown in Figs. 3 and 4. Distribution of temperature in calm condition is drawn in Fig. 4 by a composite map method, as data were not available for actual calm condition. The results always show the existence of city temperature though the value of it seem to vary with the difference of season and the variation of weather condition. Above all, the effect of wind is apparently perceived on the temperature distribuion in Fig. 3. Then, the effect of wind is analyzed in detail. Temperature distribution in calm condition has a relatively close correlation with the map for the distribution of building coverage in Fig. 2. The area of the highest temperature situates at the busiest part of the city in calm weather. In windy condition, however, location of the area of the highest temperature removes leeward in the urban area, as shown in Fig. 4. (Arrow indicates wind condition and dots represent observation points. The top of arrow shows the position of the center of the highest temperature area for corresponding condition.) Moreover, wind effect is vividly perceived in Fig. 5 that shows the departure of temperature distribution in windy condion from that of calm weather. Relatively cool air from the surrounding country flows into the urban area through area of low-rate building coverage. Finally, the relationship between the city temperature, defined by the difference of maximum temperature observed in the urban area from minimum temperature that represents the surrounding area, and weather factors expressed by the records of the Kumagaya Local Meteorological Observatory is represented in the linear empirical formula by least square method. D=4.21-0.08N-0.12n-0.52V+0.01e-0.04T (night)