On the first visit by a French prime minister to Lomé since Michel Rocard went there 27 years ago, Valls said France had made a mistake in not showing enough interest in the country.
"Togo is changing," he said while meeting French expatriates on Friday evening. "And, even if the challenges are there - I'm thinking of the rule of law, institutional reform where progress is still needed - it is changing in the right direction."
Valls was speaking after meeting President Faure Gnassingbé, who succeeded his father with the support of the army in 2005.
The tour aims to reassure countries that have felt forgotten by France over the past few years, support democratic change and strengthen trade ties, a Valls adviser told the AFP news agency.
"I am moved by a conviction that is growing ... Africa is for us the continent of the future," the French prime minister said and he slipped in a dig at former president Nicolas Sarkozy, who is currently campaigning to win back his old job next year.
French presidential election
In a reference to Sarkozy's 2007 declaration in Senegal that Africans "had not sufficiently entered into history", Valls told his audience that Africa "is more than ever in history .... has never left history".
Before leaving for Togo, Valls had told a journalist he was angry about François Hollande's publication of a controversial book of interviews Un Président devrait pas dire ça (A President shouldn't say that), which appears to have further harmed the president's chances of being reelected.
"Manuel Valls does not say clearly that he could be a candidate in 2017 in François Hollande's place," comments RFI's website in French. "But whenever the chance presents itself, as here in Lomé, he adopts an increasingly presidential tone."