The 51-year old man accosted the girl as she waited for her school bus in the Baden-Württemberg city of Tübingen, on Thursday morning, news magazine Der Spiegel reported on Saturday.
He enticed her into his car and drove her towards Baden-Baden, while he rang her family to demand several million euros in various currencies for her safe return.
The girl's parents called the police, who tracked the kidnapper and his hostage to Freudenstadt.
A special armed police commando freed the girl and arrested the man at around 8pm on Thursday after tracing a further telephone conversation with the family.
The kidnapper told investigators he had been planning to take the schoolgirl hostage for some time and had been watching the house of her wealthy father, Der Spiegel said.
But the public prosecutor told the media on Friday, “There is no private or professional connection between the man and the family.”
The man now faces prosecution and if convicted, could be jailed for up to 15 years in prison for kidnap and blackmail.