The Frenchman, who is expected by some to rival Sepp Blatter for the FIFA presidency in 2015, believes an increase in teams would only add an extra three days to the tournament's running time and would ensure better representation for non-European confederations.
Blatter recently spoke about Africa's under-representation at the showpiece, but rather than take places away from Europe, which sends 13 teams, Platini believes expansion is the way to go.
"It's good for everybody," Platini told The Times. "I totally agree with Mr Blatter that we need more African and Asian (countries). But instead of taking away some European, we have to go to 40 teams in the World Cup.
"We can add two African, two Asiatic, two American and one from Europe. I support this idea totally."
Platini believes the growth of FIFA in recent decades justifies a bigger World Cup.
"Football is changing and now we have 209 associations," he said. "There are more countries so why reduce? Forty is not so bad.
"You have three days more of competition and you make more people happy."