According to the United Nations World Happiness Report, Japan's happiness level is not very high, and its "freedom of choice in life" tends to be low. Since the 1970s, one of the important themes in studying happiness has been that the sense of happiness does not necessarily correlate with income level. In this research, we surveyed 20,000 Japanese people and asked various questions to analyze income, educational background, health, human relations, and self-determination as explanatory variables. As a result, in terms of age, we found a U-shaped curve in which happiness falls in middle age, and in relation to income, the subjective feeling of well-being does not increase as income increases. In addition, self-determination has a stronger influence than income and education as a factor that determines happiness, following health and human relations. It appears that deciding by oneself will enhance the motivation and satisfaction of action that one has chosen, which will lead also to a higher degree of well-being. It is worth noting that people with high self-determination have a high degree of happiness in Japanese society where freedom of choice in life is considered to be lower.