Japan‘s food self-sufficiency ratio was 79% in 1960, and this ratio compares favorably with that of other advanced countries with similar farmland endowments. But it fell most rapidly of all major developed countries in the last 45 years, and became the lowest among countries with more than 100 million in population. In this paper, the mechanisms of the decline in the food self-sufficiency ratio in the last 45 years were examined, and it was pointed out that epoch making events such as drastic change of dietary habits under a rapid economic growth and drastic appreciation of the yen against the US dollar were major causes of the sharp decline in the food self-sufficiency ratio. Some preliminary examinations regarding the future food self-sufficiency ratio was carried out based on some assumptions. It was found that if the calorie supply from domestically produced food follows the trend of the period 1996 - 2006 the food self-sufficiency ratio will stay at 39% or decline slightly during the period 2005 - 2015. These projection results imply that calorie supply from domestically produced food has to be increased considerably in order to raise the food self-sufficiency ratio to 45% by 2015.