Schumacher is set miss the rest of the season with a back injury

Schumacher, who had been widely expected to leave Williams for Toyota, has signed a three-year deal with the Japanese team.

The German might not get to race again for Williams after fracturing vertebrae at the United States Grand Prix.

Toyota boss Tsutomu Tomita said: "He's proven himself to be extremely quick. I'm sure his vast experience will be extremely beneficial to our team."

Toyota's current drivers Olivier Panis and Cristiano da Matta are not expected to have their contracts renewed at the end of the season.

Profile: Ralf Schumacher

"We have not finalised who will partner Ralf in 2005, and this is something we are in no rush to decide on," added Tomita.

"We are happy with the job that Cristiano and Olivier are doing for us and both of them are under consideration for the remaining race seat next season.

"There are still eight races of the season to go and everyone at Toyota is fully focused on improving our level of performance to gain as many championship points as we can."

Ralf has made a steadfast contribution to the team, with some truly spectacular high points Sir Frank Williams

Toyota have the second biggest budget on the grid behind world champions Ferrari, but are currently seventh in the constructors' championship with just eight points.

Panis has five and Da Matta three.

Schumacher's departure from Williams means the team needs to find two drivers for 2005 as Juan Pablo Montoya is leaving for McLaren.

"Ralf has made a steadfast contribution to the team over the past five years, with some truly spectacular high points," said Williams team boss Sir Frank Williams.

Schumacher made his Formula One debut with Jordan in 1997 and has won six of his 124 Grands Prix, all with Williams.

BMW motorsport boss Mario Theissen said the decision not to renew the driver's Williams contract had been mutual and came after long and intensive negotiations.