The fact that individual investors are betting big on a market trend underscores their conviction that the Japanese currency will slip further.
"With the trend for a weaker yen becoming clear amid the U.S. economic recovery and other factors, retail investors' expectations for profiting are growing," says an official at CyberAgent FX Inc.
A survey this month by the Gaitame.com Research Institute shows 67% of investors expect the Japanese currency to weaken over the next month, up 10 points from a February poll.
The yen strengthened against the dollar Thursday in Tokyo, but selling by individuals capped the Japanese currency's gain.
Many market players contend that individual traders' selling will limit the yen's upside. But profit-taking could emerge once the currency weakens sufficiently.
"Yen-buying to lock in profits will likely come in once the exchange rate nears the psychological barrier of 85 yen to the dollar," Takuya Kanda at the Gaitame.com Research Institute said.