1127 GMT June 17, 2018
According to Statistics Korea, the average earned income of such households stood at little over 3.4 million won ($3,150) in the three-month period, down 3.1 percent from a year earlier, according to Yonhap.
This drop is the most serious since the agency started compiling such data in 2003. The last significant drop in numbers for this group took place in the third quarter of 2009 when earnings backtracked 2.9 percent in the wake of the global financial crisis.
Such households have long been considered the backbone of South Korean society and have been characterized as being very economically active, as well as generally having high levels of income and robust consumption compared to other groups.
Some economists here attributed the decrease to the weak job market and the drop in household members' combined earnings compared to the past.
"Because this group includes people in their late 40s whose children are starting to join the workforce, the overall income of such households tended to be high," an observer said. He pointed out, however, that a rise in unemployment among the country's youth may have affected earnings.
In addition, employment data showed that there was noticeable drop in people in their 40s being hired in the restaurant, catering, liquor and accommodation sectors compared to other age groups, and that may have impacted the numbers. The poor showing is related to a general weakness in hiring by these industries late last year.
In December the total number of people working in related businesses was down 49,000 or 2.1 percent on-year. This is the sharpest drop since the 71,000 decrease reported for May 2011.
These businesses are often hit by slowdowns in the economy, as they usually hire irregular workers who can be easily dismissed.
In related news, the government said that while household income did not do well in October through December, it is not easy to determine the exact cause.