Fifa counterpart Sepp Blatter recently spoke about Africa and Asia's under-representation at the showpiece.
But rather than reduce Europe's finals quota of 13 teams, Platini feels 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."
He continued: "Football is changing and now we have 209 associations. 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."