Masanao Yamada is waiting for an opportunity to buy dollars.

The 39-year-old insurance salesman is part of a growing Japanese army of individual investors who have emerged as a force in foreign exchange markets in recent years as they have sold low-yielding yen to buy into the currencies of countries with higher interest rates. The sort of highly-leveraged foreign exchange trading practised by Mr Yamada has become so popular among individual investors that the Bank of Japan, the central bank, has been monitoring trading daily.