The former premier's health condition is good and he is focusing on the proceedings launched against him, Kneber said.
Sanader has not complained about the conditions in the prison.
Praising Sanader for his behaviour, the prison warden said that he was treated in the same way as the other inmates.
Asked how photos of Sanader in his prison cell could appear in the Croatian media, Kneber said he did not know how that happened.
He ruled out the possibility that some prison staffers took those pictures and added that prisoners could not do it either as they were not allowed to have cellular phones or other technical equipment.
Sanader was arrested in Austria on 10 December on an international warrant issued by Croatia, where he is wanted on corruption charges.
In the meantime, Austrian prosecutorial authorities launched an investigation into a money laundering case via a Tyrolean bank implicating Sanader.