In seeking retirement security, participants in defined contribution pension plans would be expected to have sufficient knowledge and to construct an optimal investment portfolio. But even after receiving financial education and understanding the need to hold equity assets, they often concentrate their portfolios in riskless assets. Prior studies also suggest that a significant group of participants lack the interest needed to maximize their retirement assets. Using a statistical procedure known as quantification method III, we attempt to segment the participants of Japan's defined contribution pension plans into four clusters according to their dispositions toward current market and economic conditions, attitudes toward risk taking with equities, and attention paid to retirement planning. Our analysis found that some participants lacked planning for retirement and were indifferent to their portfolios, which means that it is necessary in the next step of our study to consider any new countermeasures for such participants.