The Nikkei has dropped again today (March 28th), falling by more than one per cent on the start of the day's trading.
It fell by 1.3 per cent to 12,335.96, remaining some way below its five-day moving average of 12,437.27.
Stefan Worrall, director of cash equities at Credit Suisse in Tokyo, told Reuters that some investors have taken their profits out of the index and this has resulted in the drop.
He explained that the wider market has been performing very well for the first quarter of the year, so it is only natural there would be a drop-off now.
The fall could also be a reaction to comments made by the Bank of Japan's new governor, Haruhiko Kuroda, who has stated the country's debt levels are unsustainable.
Japan's public debt currently stands at about 230 per cent of its GDP.
"I too believe that is extremely high and this situation is abnormal and not sustainable," Mr Kuroda said at a parliamentary session.
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