Mobsters of Japan's top underworld syndicate have become the second-largest shareholder in a huge textile company in what police say is the largest known case of gangster activity on the Tokyo stock market.

Police and company sources said Wednesday that gangsters of the 30,000-member Yamaguchi-gumi syndicate have been quietly buying shares in Kurabo Industries, one of Japan's most venerable textile companies.A police official in Osaka, the western Japan city where Kurabo is based, said the stock buying itself is not under investigation because there is no evidence that any laws were broken.

A National Police Agency official, however, said police in Osaka and several other jurisdictions have been asked to gather information on the deal to help the agency keep tabs on underworld income sources.

Large-scale transfer of Kurabo stock began in late August. By late September, Tensho Enterprises had purchased 15 million shares, or 5.6 percent of all outstanding issues, said a Kurabo official who spoke on condition of anonymity.

Tensho, also based in Osaka, operates from a small apartment. It was formed by Yoshio Azuma, boss of the Yamaguchi-gumi subgang named Tosei-kai, just one month before the buying began, police sources said.

Tensho's stake, valued at $157 million as of Oct. 31, makes it the second-largest shareholder in Kurabo, which was founded in 1888 and has overseas offices in Germany, the United States and Hong Kong. Kurabo also is involved in a joint venture in Britain.

Police said they did not know whether the mobsters were buying the shares simply as an investment or to launder money gained from illegal activities such as extortion, prostitution and gambling.