Nearly one in every six Japanese lives in poverty, one of the highest rates among developed countries, according to the latest survey by Japan's welfare ministry.
In Japan's first official calculation of its relative poverty rate, the ministry said 15.7 percent of Japanese people lived on less than half the median disposable income in 2006.
The figure, based on national statistics of income in 2006, was up from a figure of 14.6 percent for 1997 according to the newly released ministry data.
"I want to implement policies to improve the figure, with child-raising allowances and other measures," Nagatsuma said.
The ratio could be worse by now as Japanese workers' salaries have fallen amid the economic slump following the 2008 global financial crisis.
The centre-left government, which ousted conservatives in August elections, has promised family-friendly policies, including a monthly allowance to households with young children.
An OECD report showed that Japan had the fourth-highest relative poverty rate among 30 member countries in the mid-2000s.
Japan's rate came to 14.9 percent in 2004, behind worst-ranked Mexico with 18.4 percent, Turkey with 17.5 percent and the United States with 17.1 percent.
The OECD report also showed the poverty rate for working single-parent households was very high in Japan, reaching 58 percent, far above second-worst Luxembourg with 38 percent.
The Japanese ministry has not calculated a poverty rate for single-parent households.
Nagatsuma has said he plans to reinstate an extra allowance to financially strapped single-parent households, possibly in December.
The allowance was gradually reduced from 2005 and completely scrapped earlier this year under the previous governments' policy of putting more emphasis on job training to help single parents earn money by themselves.