Japan's National Tax Agency believes that hundreds of people last year earned significant incomes from trading in digital currencies.
The data is based on 2017 tax returns.
At least 331 people reported making at least 100 million yen, or about 910,000 dollars, from cryptocurrencies.
The officials say the trend reflects the sharp rise in prices of Bitcoin and other virtual currencies last year.
An expert says the high-income investors are a tiny minority of all the traders in Japan. The expert says they managed to acquire the cryptocurrencies before prices started to take off.