Nomura Holdings Inc. has announced that it is set to replace its chief executive officer and chief operating officer following revelations of insider trading. The leading brokerage has also worked out measures to prevent a recurrence of such wrongdoing after admitting that there is a possibility that more information on companies' plans to increase its capital was leaked to outsiders in addition to three confirmed cases. The company appears poised to make efforts to restore the public's trust in it.

However, its response to the incident has not given the public the impression that it is determined to change its ways. The two Nomura executives appear to have reluctantly decided to step down -- due to a loss of customers and a plunge in the company's share prices following the scandal.

When it announced fresh cases of alleged insider trading, the company merely stated: "We confirmed multiple cases in which we have deemed that there is a high possibility that insider information was handed over" to customers. However, the brokerage stopped short of announcing the details of these cases, such as who was involved, the type of issue, and how many illegal acts had been confirmed.

The problems involving Nomura Holdings are particularly serious on several points. First, Nomura, which should be contributing to the development of the stock market as a leader in the industry, has been repeatedly involved in acts that have damaged the public's confidence in it.

Nomura drastically reshuffled its board following revelations that it had illegally paid off a corporate racketeer in 1997. At the time, it decided to fundamentally reform its corporate culture, but insider trading involving Nomura officials came to light on three occasions -- in 2003, 2008 and 2012.

Needless to say, it is impossible to eradicate illegal acts involving individuals who lack a law-abiding spirit. However, the latest scandal has revealed that the company as an entity gave preferential treatment to certain customers, just like in the racketeer pay-off case. This is fundamentally different from wrongdoing by individual employees. Nevertheless, Nomura has been slow to respond to the incident and appears unenthusiastic about getting to the bottom of the scandal. It may be futile to place hope in Nomura's self-purification ability.

If so, there is no choice but to increase outside pressure on Nomura Holdings. The entire industry should consider voluntary rules under which those involved in serious wrongdoing would be permanently expelled from securities markets. Administrative sanctions should also be toughened, and criminal punishments be meted out to violators while the inspection system is strengthened.

Nomura is not the only brokerage that has been involved in insider trading in connection with companies' increases of capital. Daiwa Securities Group has announced the results of its in-house investigation into employees' leak of insider information and punitive measures it has implemented against executives over the case.

The Diet should launch efforts to expose insider trading involving brokerages and their employees by summoning top executives of these companies and others to testify over these cases in the Diet.