This paper first examines energy (or fuel) poverty in Japan from 2004 to 2013, especially around the time of the 2011 Great East Japan Earthquake (GEJE). To analyze the issue, the paper employs various poverty and vulnerability measures with the assistance of our unique dataset. The results indicate the aggravation of energy poverty among lower-income and vulnerable households during the past decade, resulting from both the escalation of energy prices and lowering of income. The analysis also employs a new decomposition technique and identifies the explanatory factors associated with the increase in energy poverty. These results suggest there were major changes in the forces driving the increase in energy poverty before and after the GEJE. After 2011, income alleviates energy poverty in Japan, with energy prices becoming the main driving factor.