This study uses the Gini coefficient to analyze farm household income inequality and decomposes the inequality by farm types during 2008~2017. The Gini coefficient is decomposed into three elements: between-groups, within-groups, and residual term contributions, and the farm households are classified by farm owner’s age and standard farm size. This study shows that the Gini coefficient has not changed significantly in the last 10 years. However, the relative contributions of the elements have changed significantly due to the structural change in agriculture: the aging of farm owners and the decrease in farm size per household. Specifically, the relative contribution of small and older farmers to the Gini coefficient has increased over time.