Nomura CEO Kenichi Watanabe has resigned in the wake of an insider trading scandal at Japan’s biggest investment bank.

Watanabe announced his resignation at a press conference Thursday in Tokyo. Takumi Shibata, another top executive at the bank, has also resigned.

Watanabe, 59, will be replaced by Koji Nagai, the president of Nomura Securities, which is part of the Nomura banking empire.

Japan’s financial regulators are investigating Nomura Securities for leaking information to clients ahead of planned securities offerings by energy company Inpex, Mizuho Financial Group and Tokyo Electric Power Co. in 2010.

Nomura has admitted that some its personnel were involved in leaking inside information.

Watanabe had led Nomura as CEO for four years.