The Sea of Ariake is the bay that has the greatest tidal range in Japan and has some vast tidal plains. Investigations in the previous studies on transformation of land and sea breezes were discussed only in terms of synoptic scale wind and orographical effects. Tidal wind, which blows in accordance with the ebb and flow, is said to be observed on a calm weather, however the effects of tide on land and sea breezes were not known. The purpose of this paper is to describe the general characteristics of land and sea breezes in the summer period on the Tukushi Plain that faces the Sea of Ariake, and to clarify the tidal effects on land and sea breezes. The Tukushi Plain is surrounded by hills on three sides, and two valleys run the northwestern and northeastern parts of the plain (Fig. 1). The results obtained in this study can be summarized as follows: 1. Sea breeze starts earlier in the seashore area by one to two hours than on the sea and in the inland area (Fig. 3). 2. In the Tukushi Plain, breezes of two different direction can be seen in the evening and night. They blow parallel to the two valleys along NW to SE and NE to SW direction, respectively. Northwesterly wind comes to blow around 4 p.m. and northeasterly land breeze prevails in the middle of night (Fig. 4). 3. With regards to the tidal effects on land and sea breezes, it was found that northwesterly which begins to blow in the evening is transformed in accordance with a tidal cycle (Fig. 5 and Fig. 6). In the north coast of the Sea of Ariake, evening westerly from northwestern valley is stronger prevails at flowing period than ebbing period. On the contrary, southerly prevails at flowing period and westerly appears at ebbing period on the sea. Therefore, it can be concluded that the path of northwesterly from northwestern valley migrates northward or southward in accordance with flowing or ebbing of tide (Fig. 7).