Harry Potter and the Philosopher's Stone, the first in the series charting the adventures of a young orphan with magical powers, has sold 2.5 million copies here since the Japanese translation was released in December 1999.
"We plan to release 800,000 copies for the first print, and are able to print a further 200,000 any time," said a spokeswoman for the publisher, Say-zan-sha Publications.
"We are getting so many inquiries - we have been getting responses from various people, regardless of their sex or age," she said.
Harry Potter and the Philosopher's Stone, the first in the series charting the adventures of a young orphan with magical powers, has sold 2.5 million copies here since the Japanese translation was released in December 1999.
Sales reached 1.8 million copies for the second book, Harry Potter and the Chamber of Secrets, released in September 2000.
World record
The Prisoner of Azkaban is the third in the Harry Potter series.
The books are priced at 1,900 yen (£10.75) each and translated into English by the president of publisher Say-zan-sha, Yuko Matsuoka.
The series, written by British author J.K. Rowling, has sold more than 100 million copies globally, setting a world record.
In Germany, fans waiting for the release of Harry Potter and the Goblet of Fire in October 2000 attempted to publish an unofficial translation on the internet.
In France, the publication of the same book made the front page of several newspapers.
And in China, the first three Potter books alone have sold 1.3 million copies.
A film based on the books is due for simultaneous release in Britain and the USA on 16 November.
It stars 11-year-old Daniel Radcliffe as the young wizard, supported by a cast including Dame Maggie Smith, John Hurt, Robbie Coltrane and Emma Watson.