The 48-year-old, identified only as Detlef S, went on trial in the western city of Koblenz, accused of forcing his stepdaughter, now in her late 20s, to bear his children and of brutally abusing his daughter and stepson.
Dressed smartly in a red jacket, blue shirt and colourful tie, S showed no emotion as the charges were read out and did not speak. But his lawyer, Thomas Dueber, told the court, "He would like to clarify that he is the father of the seven children of the co-plaintiff (his stepdaughter). But he denies the charges made against him."
In line with German privacy laws, the defendant's full name was not given in court. Paternity tests have proved virtually 100 per cent that the unremarkable man with glasses and greying, receding hair, was the father of the seven children. An eighth child died shortly after birth and was not examined.
Several German media have compared the case to that of Austrian Josef Fritzl, who held his daughter Elisabeth as a sex slave in a cramped dungeon for 24 years. Fritzl raped Elisabeth thousands of times, fathering seven children with her and letting one of the newborn babies die. He was sentenced to life in prison in March 2009.
In total S is charged with 350 counts of sexual assault and grievous sexual assault of minors. He is also accused of prostituting the stepdaughter and his biological daughter out to others, allegedly while he watched.
A verdict is expected on February 25 S faces 15 years behind bars if convicted. The stepson, identified as Bjoern, told reporters outside the courthouse that authorities had failed to do their job properly and missed telltale signs of abuse in the house, alleged to have gone on between 1987 to 2010.
"If you are a trained social worker you are supposed to go there and interview the victims without the perpetrator being present, and not all together," he said.