Henrik Landerholm is prosecuted for negligence with secret information since it has been revealed that he left secret documents in an unlocked cabinet.
Landerholm risks fines or imprisonment for up to one year, but denies the crime.
Nothing has emerged that changes our attitude, that he has not committed a crime, says his defense attorney Johan Eriksson.
The trial, in Attunda district court in Sollentuna, started quietly on Friday with a so-called evidence collection.
On Monday, when the main hearing begins, among others Henrik Landerholm himself will be heard.
I have nothing new to say other than what I will say today in the trial, he says on the spot in the district court.
In addition to the revelation about the forgotten documents at the conference center, it has also emerged that Henrik Landerholm on one occasion forgot a notebook at Sveriges Radio and forgot his mobile phone at the Hungarian embassy.
Henrik Landerholm left the post as national security adviser when a criminal investigation against him was initiated in January this year.
He is now prosecuted suspected of negligence with secret information.
According to the prosecution, he "through gross negligence, unauthorized, disclosed" secret information in documents that he left behind at a conference center outside Stockholm in March 2023.
Landerholm denies the crime.
