The income of households headed by those in their 40s has declined for the first time.

According to Statistics Korea on Monday, breadwinners between the ages of 40 and 49 brought home an average of five-million-52-thousand-153 won, or four-thousand-315 U.S. dollars a month, in the third quarter. 

The amount was down by one-thousand-569 won from the same period last year.

It is the first time the income of such households fell year-on-year since the statistics agency began compiling related data in 2003.

Until the second quarter of last year, the households had seen their income increase by five percent or more from a year earlier. However, the margin of income growth dropped to one-point-63 percent in the fourth quarter of last year before further falling to zero-point-two percent in the second quarter of this year.

Economic experts say it can be ill-boding signs for the South Korean economy given that households led by those in their 40s play the most active role in increasing income and consumption for the country.