On Friday, as part of an expanded probe into corruption surrounding the 2020 Tokyo Olympics.
Local news stations aired footage showing prosecutors from Tokyo's district office and representatives from Japan's Fair Trade Commission.
Dentsu is the undisputed leader in the Japanese event planning, marketing, and PR industries.
A former Dentsu executive named Haruyuki Takahashi has been detained four times in the last several months on suspicion of accepting bribes .
According to Japanese media, the new probe is focusing on allegations of bid manipulation by firms hoping to work on test events.
According to the Nihon Keizai Shimbun and other publications, nine corporations and one organisation participated in the bid-rigging scheme.