French billionaire Vincent Bolloré has been detained for questioning by anti-corruption police near Paris.
His holding company the Bolloré Group has denied any irregularities.
It is alleged that a subsidiary helped two African presidents win power in return for lucrative contracts.
Two rival firms have taken the Bolloré Group to court over the concessions.
Mr Bolloré's business empire includes shipping, advertising, construction and media and has large interests in Africa. He is one of France's best-known businessmen.
Investigators are looking into allegations that his Havas advertising agency provided discounted communications advice to Guinean President Alpha Condé and Togolese President Faure Gnassingbé at election time in return for the Bolloré Africa Logistics company being given licences to operate container ports in Conakry and Lomé.
All parties deny the allegations.
After the election in Guinea, Mr Condé terminated the contract of Conakry port's existing operator and gave it to the Bolloré Group.
A spokesman for the government of Guinea said there was nothing wrong with the contract for the shipping container terminal.
The Bolloré Group says that its long record of investment in Africa was already sufficient grounds for it to have been awarded the licences.