CSK Corp. will become the largest stakeholder in Cosmo Securities Co. by purchasing a stake of roughly 50 percent in the brokerage house from Resona Holdings Inc., the three firms officially announced Thursday.

Resona Holdings, the top shareholder in Cosmo Securities, said it will sell about 83 percent of the group's equity stake, or 210 million shares, in Osaka-based Cosmo Securities to CSK in April.

CSK is a Tokyo-based computer systems consulting firm.

According to Resona Holdings, the financial group will launch the sale as a means of stepping up its restructuring efforts by reducing its number of affiliated companies.

Resona Holdings has been trying to concentrate on its banking business since it received a 1.96 trillion yen public fund injection in June.

Under the deal, CSK will launch brokerage activities by using its accumulated knowhow in the information technology business.

"Through the tieup between CSK group's services and Cosmo Securities' management resources, we hope to create a pioneering securities company that will enable us to expand our business and to consolidate our management base," Takahiro Suzuki, chief financial officer at CSK, told a news conference.

Takashi Motohashi, executive managing director of Cosmo Securities, told the same news conference: "We judge that we would be able to improve our corporate value by improving our services to our clients, develop new financial products and strengthen our risk control and compliance system through a strong collaborative relationship with CSK."

Cosmo Securities reported a net profit of 1.3 billion yen during the half-year period through September.