A police cortège accompanied the 33-year-old right-wing extremist as he was driven from Skien prison at 11am before arriving at Ila at 1.10pm.
Breivik, who has admitted to killing 77 people in twin terrorist attacks last July, will learn of his fate when an Oslo court announces its verdict on Friday.
“We’re ready to take in Breivik regardless of whether he is sentenced to prison or compulsory psychiatric care,” said Ila director Knut Bjarkeid in a statement.
In the case of an insanity verdict, staff from Dikemark psychiatric hospital will likely be entrusted with his care at a special one-man hospital within the Ila prison grounds.
The prison is also working on the construction of a new high-security wing where Breivik will later be held if the court finds he was sane when he set off a car bomb outside government buildings in Oslo before embarking on his shooting rampage on the island of Utøya. Work on the new block is expected to be completed next autumn.