The writer has analysed the distribution of the air temperature in April in a coastal area, chiefly through the comparison between those of Hiroshima and Kure, which are situated on the northern coast of the inland Sea of Seto, the results being as follows. So far as the minimum air temperature is concerned, Hiroshima shows a lower value than Kure, and the differance is conspicuous on a clear night when it increases rapidly (Fig. 1 III, Fig. 2). The reason why such a rapid increases takes place is that the discontinuous decline of the temperature happens in Hiroshima (Fig. 3 II), while the curve of the night cooling in Kure shows a continuous one (Fig. 3 I). The former is sometimes caused by the land breeze, streaming out from inland (Fig. 3 IV), which is not always the sole factor (Fig 5). But this phenomenon is not observable when the sea breeze blows. The valley of R. Ota flowing into the sea at Hiroshima forms a favourable passage way of an air stream to Hiroshima, along which blows the air cooled in inland, carrying the front with it (Fig 8). On the contrary, Kure being surrounded by the hills in the rear, the sudden fall of the temprature is seldom brought about, even when the land breeze begins to blow. Thus Kure retains the climatological characteristics a sea coast shows, while Hiroshima is covered with the inland stream with the result that both of the areas are influenced by the heterogeneous air-masses. The difference of the tem-perature is caused in this manner, and from such an angle can be grasped-the distribution of the nocturnal air temperature in a coastl area.