Japan's biggest advertising company Dentsu has replaced its CEO
Yamamoto is currently a senior vice president at Dentsu and has been at the company since 1981. He will move into his new role on January 23.
He takes on leadership of a company that his been plagued with issues over the past year.
Last month, Japanese government officials filed papers with the prosecutor's office, which could see criminal charges brought against Dentsu and the managers of Matsuri Takahashi, a 24-year-old Dentsu employee who took her own life in December 2015. Japanese labor inspectors ruled in September that her death was caused by "karoshi," a Japanese word meaning death by overwork.
In announcing his resignation, Ishii said in a news conference in December he was taking responsibility for the work-related suicide and for failing to achieve a "dramatic reform of overwork." Ishii had been the company's chief executive since 2011.
Earlier this week, Dentsu revealed the outcome of its investigation into whether its Japanese subsidiary over-charged clients for digital advertising services. It discovered 977 transactions "unsuitable for business practice" had been carried out between 2012 and 2016, including 10 cases of over-billing. The total transactions concerned amounted to ¥114.82 million ($1.01 million) in fees.
In a statement announcing his promotion, Yamamoto said: "My mission is to re-establish trust in Dentsu in Japan, and build a sustainable growth path for the long term. I believe it will become a reality with the improvements we are making to create a more flexible working environment where our diverse talents will thrive to help create value for our clients and professional fulfillment for our people."
Dentsu also announced two other senior appointments on Thursday. Shoici Namakato - currently senior executive vice president and CFO - will become representative director, senior executive vice president, and chief financial officer. Yoshio Takada - currently director and executive vice president - will become a representative director and executive vice president.