The funding for police comes out a $2bn pledge by Japan
Japan has said it will pay the salaries of about 80,000 Afghan police officers for the next six months as part of its drive to help regeneration there.
Japan would also help fund the construction of schools and hospitals and support teacher-training, a foreign ministry official in Tokyo said.
Tokyo has pledged about $2bn in Afghan reconstruction funds since 2002.
Separately, New Zealand announced it would keep its deployment of about 140 troops in the country for another year.
Japan's support for Afghanistan is likely to be discussed when Japanese Prime Minister Taro Aso meets US President Barack Obama in Washington later on Tuesday.
He will be the first foreign leader to meet the new US president at the White House.
Japan has no troops in Afghanistan but has maintained a refuelling mission in the Indian Ocean in support of the US-led "war on terror".
Tokyo has spent almost $1.5bn of the money it pledged back in 2002.
Mr Obama has said Afghanistan is a priority issue in his foreign policy and has approved 17,000 additional US forces.
Meanwhile, New Zealand's Prime Minister John Key said his country would extend its troop commitment in Afghanistan to September 2010.
Its soldiers primarily work in reconstruction in Bamiyan province.