Mitsuhei Obuchi, mayor of the town of Nakanojo in Gunma Prefecture, North of Tokyo, holds 270 shares, or a 0.02 per cent stake, in NTT Docomo, making him the second-largest individual shareholder.

NTT Docomo, a unit of Nippon Telegraph and Telephone Corp (NTT), announced earlier on Monday that its shares, which will debut on the Tokyo Stock Exchange's first section on October 22, will be initially offered at 3.9 million yen.

The price was near the upper end of the indicative price range between 3.3 million to 4.3 million yen announced by NTT Docomo in late September.

In what would be one of the world's largest initial public offerings, NTT group is due to raise a total 2.13 trillion yen.

Under the IPO, Docomo will issue 327,000 newshares, raising 1.28 trillion yen, while parent company NTT will raise about 850 billion yen throughout the sale of its 218,000 Docomo shares. NTT will reduce its holding in Docomo to 67.1 per cent from the current 95 per cent.

Japan's main opposition Democratic Party said in late September that it would investigate how the Obuchi's brother became a major shareholder in NTT Docomo.

Yukio Hatoyama, a Democratic lawmaker, did not say at that time what possible irregularities his party hoped to prove.

He also said that there were "names related to politicians" on the list of Docomo's individual shareholders, prompting his party to conduct the investigation.

A party official told Reuters on Monday that the investigation was still under way, although making only slow progress due to prolonged political wrangling over how to solve the nation's banking problems.

An official at prime minister Obuchi's private office, meanwhile, said the brother's share purchase in the 1970s was a personal deal and hadnothing to do with the prime minister.