Josef Fritzl is facing life in prison after imprisoning and sexually abusing his daughter Elisabeth for 24 years.
He surprised his legal team in Austria when he changed his plea to guilty on all charges after being confronted in court by his daughter's testimony.
"I declare myself guilty to the charges in the indictment," he said, referring to what he called "my sick behaviour".
Fritzl acknowledged his guilt on the third day of the trial. Asked by the presiding judge why he had changed his mind, Fritzl said it was the testimony from Elisabeth.
She attended the hearing on Monday and Tuesday, the first time the 42-year-old has faced her father since his arrest last year.
He watched 11 hours of her videotaped evidence, describing how he imprisoned her in a dungeon underneath their home and repeatedly raped her, fathering seven children.
One child, a twin boy, died at three days old and the changed plea means Fritzl, 73, has admitted killing him through neglect - a charge that carries a potential life sentence.
Initially he denied responsibility for the baby's death, along with an enslavement charge. He had already admitted rape, incest, forced imprisonment and coercion.
Elisabeth was the key witness against Fritzl. She was 18 when he imprisoned her in the cramped, windowless cell he built beneath the family's home in the town of Amstetten.
Elisabeth and her six surviving children, who range in age from six to 20, have spent months recovering from their ordeal in a psychiatric clinic and at a secret location.
