He reported over 5 million yen ($48,000 USD) for utility expenses in 2005. This expense was questioned by the press, since Matsuoka had a very small office. However, Matsuoka said that it had been paid for purified water, explaining that people rarely drink tap water. On 28 May 2007, hours before facing questioning in the Diet (parliament), he committed suicide by hanging in his Tokyo apartment and died in Keio University hospital in Tokyo. Norihiko Akagi was appointed his successor on 1 June after provisional Minister Masatoshi Wakabayashi.