Japan’s Prime Minister Yoshihiko Noda said in his party’s August presidential election speech that after he lost his parliamentary seat in the mid-90s, he could have used the $100-plus monthly grant to families with children brought in by the ruling Democratic Party of Japan to help buy his two sons new pants and shoes.

A report released Friday on assets owned by members of Japan’s cabinet shows he wasn’t kidding.

The humble prime minister, who famously likened himself to a lowly bottom feeder fish called the “dojo,” or loach—as opposed to the glitzy goldfish of his rivals and successors—turns out to be Japan’s “poorest” premier since the government started disclosing assets of cabinet members and their families in 1984, with just ¥17.7 million in assets between him and his wife.

Mr. Noda’s biggest asset is his ¥10 million house in his hometown Funabashi in Chiba prefecture, located in the outskirts of Tokyo. The average price of a house in the neighborhood, according to Nomura Real Estate Urban Net is ¥20 million. The nation’s leader has a ¥33.8 million mortgage on his house.

In the column marked “Automobiles, including sailboats, airplanes, racing horses,” Mr. Noda does have a few entries, but they’re not exactly jet-set: A 1999 Nissan Cedric, a 1999 Honda Integra, and a slightly newer, 2000 Toyota Hiace minivan. Otherwise, Mr. Noda reported ¥2 million in the bank, his wife, ¥600,000. Neither he nor his family owned any stocks.

The noble title of “pauper premier” was previously held by Mr. Noda’s predecessor Naoto Kan, who cited ¥22.4 million in assets, which included land he inherited from his father. Mr. Noda, whose father was the youngest of six siblings and his mother the last of eleven, has no inheritance of note.

Cabinet members are required to disclose family financial assets first when they take office, and later when they leave. The report covers real estate, long-term deposits and securities, savings in Japan Post, loans and credit. Check and regular savings accounts are off-limits, but they also have to reveal family ownership of cars, artworks and country club memberships, without specifying their value. While rules have changed over the years, cabinet ministers began disclosing their assets in 1984 to “gain the public’s trust,” said a cabinet office official.

Mr. Noda’s Cabinet, without mega-rich ministers like former premier and original blue-blood Yukio Hatoyama (his grandfather was a three-term premier) bringing up the average asset, is likely to be one of the most modest cabinets of all: Three of 18 ministers and their families owning no property at all. The only minister to report over ¥100 million was National Public Safety Minister Kenji Yamaoka, and the cabinet’s assets averaged at around ¥50 million.