A palynological study was made of the samples taken from the Okou mire deposits in the central part of the Kochi Plain, in southern Shikoku. Two pollen zones were established in the pollen diagrams ; (1) the Castanopsis-Cyclobalanopsis zone (-250〜-90 cm) and (2) the Pinus-Cyclobalanopsis-Alnus zone (-90〜0 cm). The first zone is characterized by the dominance of the climatic climax forest in the area studied, and the second one by the fall of the natural forest and the rise of the secondary one owing to human agencies. Rice cultivation probably began during the Late Jomon Age (about 2,800〜3,000 years ago). Buckwheat cultivation possibly began during the Early or Middle Jomon Age (about 5,000〜7,000 years ago).