OSAKA -- Police are questioning a former Taiheiyo Securities Co. employee on suspicion of misusing more than 300 million yen in his client's fund, informed sources said Monday.They said the former acting sales chief at the Umeda branch here received more than 300 million yen from a client between March 1991 and March 1992 on the pretext of purchasing convertible bonds. The brokerage house is affiliated with the failed Yamaichi Securities Co.The man, 39, whose name was withheld, is suspected of using most of the client's fund for stock deals under the name of a different customer, the sources said. The client said she has deposited 3 billion yen with the stock broker since she started business with him in September 1986, but more than 1 billion yen has not been returned, the sources said.The client filed a damages suit with the Osaka District Court in October 1992 against the man, who was fired from the securities house in January 1993.