Each household owned an average of 1.076 motor vehicles as of the end of March, down 0.004 from a year earlier, according to the Automobile Inspection & Registration Information Association.
It's the fifth straight year the number has declined.
Households owned 57.89 million cars as of the end of March, up 0.4 percent from a year earlier, the association said. But the average fell as the number of households has increased faster than the number of cars since 2007.
The figure, which includes minivehicles, does not include data from households in 22 cities, towns and villages in the quake- and tsunami-ravaged prefectures of Iwata, Miyagi and Fukushima prefectures, the association said.
Although a large number of cars were damaged or washed away in the disaster, March 2010 data for the three prefectures were used for the latest survey.