The Kyodo news agency says it may be bribery, and according to local media, a consulting firm run by Takahashi is suspected of having received money from Aoki for a contract signed in 2017.
Aoki then became a sponsor of the Tokyo Olympics in October 2018.
Takahashi himself said last week that the money his company received was for consulting work.
In the same week, Aoki also issued a statement in which they did not want to comment on the payouts.
Takahashi sat on the board of the Tokyo Olympics between 2014 and 2022.
"Very sad"
Seiko Hashimoto, who presided over the Tokyo Olympics, said on Tuesday that she would cooperate fully if needed in the investigation.
- That things like this come up is very sad, she said.
It is not the first time that the Tokyo Olympics have been associated with bribery.
Tsunekazu Takeda, former head of Japan's Olympic Committee, resigned in 2019 after French authorities investigated his involvement in two payments of around 19 million kroner to a bank in Singapore before and after the IOC's vote to host the 2020 Summer Olympics (which were moved to 2021 due to the pandemic).